What is the different between primary deco is connected to the second deco device (Mesh Network Performance) like speed? *by WiFi *by LAN cable

Question 1: Is it possible to position the primary deco device adjacent to the telco modem? Is it possible that the network bandwidth will be reduced as a result of the decor? Question 2: The position

Here's my setup: ZTE UniFi Modem --> Deco x20 (primary) --> Deco x20 (room 2) --> Deco x20 (room 3) --> TV, Mobile, Labtops. - ZTE UniFi Modem to Deco x20 (primary) connects on port 1. - Deco x20 (pri