Diffusers in front of BDA's ?-Acoustics Forum-Acoustic Fields Forum

I currently have 68% coverage on 5 walls with your terrific foam . I also have 6 BDA‘s with your carbon with 4 on front wall and they’re basically 2×4 ft tall.
I will be building diffusers for the front wall but I feel starting them from 4ft off the floor is too high, as you generally recommend them at 2ft.
Will I be sacrificing the power of my BDA‘s being behind my diffusers?
Also, will I still need your foam as the front cover of my BDA seeing that the top 2 ft will be blocked by the diffusers?

Thanks again for sharing your knowledge and making us realize how room acoustics can have such a profound effect on the music we listen to.

Frank A