dnd 5e – How can I adjust this squatting rule to balance it?

My ranger uses a light crossbow. A few sessions ago, he has his move and his attack as "I move there and squat before the attack." In characterBefore, he taught the others that it's better to squat, because it does not leave so much free space. I am impressed, agree and grant disadvantages in attacks on crouched targets.

Disadvantage of all remote combat squats against crouching character, but other than vulnerable they can stand up and move without penalty.

The squatting character gives an additional 1 foot of movement per foot moved.

Now, after a few sessions, he keeps telling me that he is crouching before he attacks and before his turn. After a few sessions, I think all my assault attacks have been penalized against him, and attacks in my next round are also ridiculous.

How should I change this squatting rule to provide some mechanical advantage, but not big enough for players to abuse?