Definitely mess with window size over any other setting. The Xbox curve made me realize that low window size like 20 actually feels stronger than a window of 70. Because when inside the window you still hit the turn cap and are limited. A mouse swipe will never be able to handle aim assist because the swipe is emulating stick tilt. And there's no way to swipe consistent enough to match a stick tilt of the same value. So window size effects more than just when it kicks in. It also effects how strong the aim assist grabs. Test it out on a target at long range with flicks. Far easier to flick on low window and its more magnetic where high window causes just a larger window of inconsistent movement.
Exactly. But the aim ease in can affect when the aim assist actually starts kicking in so its good to mess with both to your liking

The way the aim assist ease in works if no one knows is the higher the value, the closer to the target the aim assist will start kicking in harder. For example, if u use 100 aim window, and 0 aim assist ease in, the second ur crosshair touches the aim window you will have 100% aim assist strength, but if u use 100 window and 100 aim assist ease in, the aim assist strength will be really weak the second u hit the window, and slowly ramp up till ur on target to max strength once u hit the target. Its good to find a good balance between the 2 so your flicks are still pretty consistent, but u also keep good tracking when needed

Good example is hanzo, where sometimes u track, and sometimes u flick.