Seeking advice on skyline diffuser size and placement

I’m in the process of improving the acoustics in my listening/living room and would appreciate some guidance from those with experience.

I’ve ordered cork panels for the TV wall and the light grey wall behind my left speaker, and now I’m focusing on building skyline diffusers for the dark grey wall directly behind each speaker. I’m uncertain about the optimal dimensions for these diffusers. For context, you can view my virtual system.

My setup is in an open space where my living room, kitchen, and dining area are all one room. My listening position is ~14’ from the TV / speakers. I already have GIK Acoustics 4" Impression Pro Series Bass Trap Diffuser/Absorbers hung at the first reflection points (or as close as possible given the limitations of the room).

Specific questions:

1. What would be an appropriate height for skyline diffusers that will be ~24 inches wide?
2. Should the skyline diffusers extend beyond the height of the speakers, or is it sufficient to align with them?
3. Would I get better results using shorter skyline diffusers (~24" tall) in combination with other acoustic treatments directly behind the speakers? If so, what complementary treatments would you recommend?

Thanks in advance for any insights!