I have a new Deco M9 Plus in a 1,500 sq ft condo.It is 1,000 MB from Webpass and when I test it from the Deco app, I get a reading of 842 Mbps down and 908 Mbps up.  However, when I connect only one device, iPhone 11 pro max, it only shows a variation of 150 Mbps to 450 Mbps right next to the main M9. If I walk to the other end of the condo (drywall and no concrete walls), it drops to double digits. I then installed the second M9 in the second bedroom. Now the second bedroom shows about 250 MB max. What am I doing wrong?

Thanks. I was hoping to get multiple devices connected with little degredation of bandwith.