InnerShadow not behaving as expected

User reported that they are trying to replicate simple raised/depressed button with altering innerShadow between 20% white(raised) and 50% black(depressed).

In Sketch this looks good(Example attached) but not correct when using innerShadow on Rectangle element in QML.

User had multiple attempts and results were:

20% opacity white shadow("Qt.hsla(0,0,1,0.2)") makes the background color DARKER. If they raise opacity to .75 the brightness is right but the saturation is down.

Users example button attached.

On line 117 the reference square does the blending the way he has expected: Lighter shade for background color. They want translucent, white inner shadow to blend like that.