diff --git a/src/compile/mark/encode/nonposition.ts b/src/compile/mark/encode/nonposition.ts
index df56da2fb2..aac6b2d447 100644
--- a/src/compile/mark/encode/nonposition.ts
+++ b/src/compile/mark/encode/nonposition.ts
@@ -6,6 +6,7 @@ import {getMarkPropOrConfig, signalOrValueRef} from '../../common';
 import {UnitModel} from '../../unit';
 import {wrapCondition} from './conditional';
 import * as ref from './valueref';
+import {isRelativeBandSize} from '../../../mark';
 
 /**
  * Return encode for non-positional channels with scales. (Text doesn't have scale.)
@@ -24,11 +25,14 @@ export function nonPosition(
   let {defaultRef, defaultValue} = opt;
 
   if (defaultRef === undefined) {
-    // prettier-ignore
-    defaultValue ??= getMarkPropOrConfig(channel, markDef, config, {vgChannel, ignoreVgConfig: true});
+    const markPropOrConfig = getMarkPropOrConfig(channel, markDef, config, {vgChannel, ignoreVgConfig: true});
+    if (!isRelativeBandSize(markPropOrConfig)) {
+      // prettier-ignore
+      defaultValue ??= markPropOrConfig;
 
-    if (defaultValue !== undefined) {
-      defaultRef = signalOrValueRef(defaultValue);
+      if (defaultValue !== undefined) {
+        defaultRef = signalOrValueRef(defaultValue);
+      }
     }
   }
 
diff --git a/src/compile/mark/encode/position-rect.ts b/src/compile/mark/encode/position-rect.ts
index e34f54d62e..a2389d355e 100644
--- a/src/compile/mark/encode/position-rect.ts
+++ b/src/compile/mark/encode/position-rect.ts
@@ -18,7 +18,7 @@ import * as log from '../../../log';
 import {BandSize, isRelativeBandSize} from '../../../mark';
 import {hasDiscreteDomain} from '../../../scale';
 import {isSignalRef, isVgRangeStep, VgEncodeEntry, VgValueRef} from '../../../vega.schema';
-import {getMarkConfig, getMarkPropOrConfig, signalOrStringValue, signalOrValueRef} from '../../common';
+import {getMarkConfig, getMarkPropOrConfig, signalOrStringValue} from '../../common';
 import {ScaleComponent} from '../../scale/component';
 import {UnitModel} from '../../unit';
 import {nonPosition} from './nonposition';
@@ -158,18 +158,17 @@ function positionAndSize(
       : (orient === 'horizontal' && channel === 'y') || (orient === 'vertical' && channel === 'x');
 
   // Use size encoding / mark property / config if it exists
-  let sizeMixins;
-  if (encoding.size || markDef.size) {
+  let sizeEncodingMixins;
+
+  if (encoding.size) {
     if (useVlSizeChannel) {
-      sizeMixins = nonPosition('size', model, {
-        vgChannel: vgSizeChannel,
-        defaultRef: signalOrValueRef(markDef.size)
+      sizeEncodingMixins = nonPosition('size', model, {
+        vgChannel: vgSizeChannel
       });
     } else {
       log.warn(log.message.cannotApplySizeToNonOrientedMark(markDef.type));
     }
   }
-  const hasSizeFromMarkOrEncoding = !!sizeMixins;
 
   // Otherwise, apply default value
   const bandSize = getBandSize({
@@ -181,7 +180,7 @@ function positionAndSize(
     useVlSizeChannel
   });
 
-  sizeMixins = sizeMixins || {
+  const sizeMixins = sizeEncodingMixins || {
     [vgSizeChannel]: defaultSizeRef(
       vgSizeChannel,
       offsetScaleName || scaleName,
@@ -203,7 +202,7 @@ function positionAndSize(
    */
 
   const defaultBandAlign =
-    (scale || offsetScale)?.get('type') === 'band' && isRelativeBandSize(bandSize) && !hasSizeFromMarkOrEncoding
+    (scale || offsetScale)?.get('type') === 'band' && isRelativeBandSize(bandSize) && !!sizeEncodingMixins
       ? 'top'
       : 'middle';
 
diff --git a/src/mark.ts b/src/mark.ts
index f80f7b2ee7..ee1a8f457e 100644
--- a/src/mark.ts
+++ b/src/mark.ts
@@ -1,4 +1,14 @@
-import {Align, Color, Gradient, MarkConfig as VgMarkConfig, Orientation, SignalRef, TextBaseline} from 'vega';
+import {
+  Align,
+  Color,
+  Gradient,
+  MarkConfig as VgMarkConfig,
+  Orientation,
+  SignalRef,
+  TextBaseline,
+  LinearGradient,
+  RadialGradient
+} from 'vega';
 import {CompositeMark, CompositeMarkDef} from './compositemark';
 import {ExprRef} from './expr';
 import {Flag, keys} from './util';
@@ -128,7 +138,7 @@ export interface VLOnlyMarkConfig<ES extends ExprRef | SignalRef> extends ColorM
 
 export interface MarkConfig<ES extends ExprRef | SignalRef>
   extends VLOnlyMarkConfig<ES>,
-    MapExcludeValueRefAndReplaceSignalWith<Omit<VgMarkConfig, 'tooltip' | 'fill' | 'stroke'>, ES> {
+    MapExcludeValueRefAndReplaceSignalWith<Omit<VgMarkConfig, 'tooltip' | 'fill' | 'stroke' | 'size'>, ES> {
   // ========== Overriding Vega ==========
 
   /**
@@ -147,7 +157,7 @@ export interface MarkConfig<ES extends ExprRef | SignalRef>
   /**
    * Default size for marks.
    * - For `point`/`circle`/`square`, this represents the pixel area of the marks. Note that this value sets the area of the symbol; the side lengths will increase with the square root of this value.
-   * - For `bar`, this represents the band size of the bar, in pixels.
+   * - For `bar`, this represents the band size of the bar, in pixels, or relative band size (e.g., `{"band": 0.5}` is half of the band).
    * - For `text`, this represents the font size, in pixels.
    *
    * __Default value:__
@@ -158,7 +168,7 @@ export interface MarkConfig<ES extends ExprRef | SignalRef>
    *
    * @minimum 0
    */
-  size?: number | ES; // size works beyond symbol marks in VL
+  size?: number | ES | RelativeBandSize; // Unlike in VG where size is only for symbol marks (point in VL), size works beyond symbol marks in VL
 
   /**
    * X coordinates of the marks, or width of horizontal `"bar"` and `"area"` without specified `x2` or `width`.
@@ -468,7 +478,9 @@ export interface RelativeBandSize {
   band: number;
 }
 
-export function isRelativeBandSize(o: number | RelativeBandSize | ExprRef | SignalRef): o is RelativeBandSize {
+export function isRelativeBandSize(
+  o: number | RelativeBandSize | ExprRef | SignalRef | string | LinearGradient | RadialGradient | number[]
+): o is RelativeBandSize {
   return o && o['band'] != undefined;
 }