A further oil brush loading quirk. It seems like even though a single brush is loaded with the same amount of paint, the total volume of paint laid down in a single stroke varies and is vastly different based on the size of the brush contact with the canvas during the stroke. This is a quirk of any brush whose size (brush contact with canvas) changes with pressure i.e. stylus or pen pressure ON.

To be fair, (with a brush with stylus pressure off) heavy pressure lays down thicker paint quickly which is good, and lighter strokes lay down shallower paint more slowly allowing longer strokes. This, I presume, conserves the volume of paint for each stroke, so that it is consistent for every stroke independent of pressure (when the stylus pressure is OFF). This is shown at the top of the pic.

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In the red rectangle are strokes with a round brush with stylus pen pressure controlling the size of the brush contact with the canvas ON. Loading on the brush was not changed and was the same for each stroke.
As can be seen in the pic, the total paint laid down is vastly different for a brush loaded with the same amount of paint, depending on the amount (size) of brush contact with the canvas. Strokes begun with a small amount of brush contact result in very little total paint being laid down, and no further handling of the brush results in the "rest" of the loaded paint being laid down on the canvas.