How do I tweak this crouching rule to balance it?

My ranger uses light crossbow, and after a few sessions now he is consistently telling me that he crouches before he attacks and before he end his turn.

Disadvantage on all ranged attacks against crouching character, but different from prone, they can stand up and continued to move without movement penalty.

Crouching character also spend extra 1 foot movement per foot moved.

After a few sessions, I think having all my readied attack against him got disadvantage, and attacks on my next turn, too, is ridiculous.

How should I modify this crouching rule so that it grants some sort of mechanical advantage, but not big enough so players can abuse it?