Rolling a ton of bunches, checking the draw on each and then immediately adjusting on the next one, attempting to calibrate. It's the only way. After enough bunches your hands will have a feel for what that leaf should feel like in your hand and how much pressure you should be applying as you bunch, depending on your situation, e.g. freehand/molded, bunch thickness, etc. This is between your hands, the world, and your central nervous system, and they have to sort it out through work.