My ranger uses light crossbow. A few sessions back, he flavored his movement and attack as "I move there, and crouch before attacking." In character, previously he taught the others that it is better shooting while crouching, because it does not leave as much open spot. Impressed, I agree, and grants disadvantage on attacks against crouched target.
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.
Now after a few sessions now he is consistently telling me that he crouches before he attacks and before he end his turn. 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?
I don’t want to just switch to using the Prone rules, because Prone gives disadvantage when attacking, which crouching shouldn't.