I purchased the 2-device pack of the Deco XE75's for a 2 story house (older, wood frame). One node (the main, connected to 800+ Mbps ethernet from cable modem) is on the first floor, the other is on the 2nd floor nearly directly above the first device. House is not wired for ethernet, so devices must use wireless backhaul. 2.4, 5, and 6 GHz bands enabled. I can actually connect via 5G to the main device from anywhere in the house with decent speeds (over 400 Mbps from desktop PC, tested with Ookla Speedtest). 

Problem 1) -- connecting to the 2nd device (which is closer to my PC) drops the connection speed to approx. 160 Mbps if using 5 GHz band...but if using 6 GHz band connection (while close to 2nd node) speed is faster than 5G direct to main device. Is there a reason for this behavior? Is there a way to remedy this slow 5 GHz speed? Not all of my upstairs devices currently support Wifi 6. Rebooting mesh network and other attempted troubleshooting steps (such as turning off the 6 GHz network to ensure that nothing other than the nodes themselves are using the band) have made no change in this behavior.

Problem 2) -- Related to the above?? My Pixel 7a phone wants to connect to 2nd node in 2.4 GHz band. Have to force 5 GHz connection in app. It does no better than approx. 160 Mbps in 5G, whether connected to to main node or 2nd node. But when connected via Wifi 6E close to main node can easily exceed 700 Mbps, and nearly 500 Mbps when close to 2nd node. Have not been able to find any way to improve connection speeds in 5G. Any ideas?

Thanks