I have 6 x20 s to cover a large three floor house - it's in the Middle East so built of thick heavy concrete with high Ceilings. I have three deco's on the ground floor, two on the 1st floor and 1 on the top floor. Generally the deco stay connected but speeds drop off very quickly. I assume it is a coverage issue. I wonder which addtional decos would give the best performance boost? More x20s or is there a newer model that would be compatible and be better. I have just updated to later firmware and the x20 were purchased in 2021.

thanks