Stooping in low corridors

[Infiniti2000]

I'm of the philosophy of: don't say Unusable; assign a penalty score instead. Even if it's -20 or -40. Choices over restrictions.

That's fine as long as you adopt a natural 20 variant. -20 or -40 could in fact be equal to -0 if you already need a natural 20 to hit. Your philosophy is the main reason why called shots do not work in D&D.

Back on topic, unfortunately vertical Space was never (properly) addressed in D&D. For the most part, I would apply squeezing rules at 3/4 to 1/2 your height and just a -2 circumstance penalty on attack rolls, reflex saves, and AC on 3/4 and up (to something less than full allowance for height).

 

[Whimsical]

Okay, I'm revising my philisophy to assigning a big attack penalty AND half damage instead of saying Unusable.