I've bought recently a deco M9+. I've got a perfectly working set up with two P7, with powerline backhaul. What is the best setup in this combination? Is that: insert M9+ as a master and behind it the P7's of is the best set up P7 en behind it the M9+.

My current setup is: groundfloor - M9+ second floor P7 and third floor the second p7.  Before the M9 my internet speed was 250 mb/s now hardly 50 mbs. What am I doing wrong.