[Support request] Front half of a 4 pot system not working

Hello, I just recently received a 4 pot autopot system and finished the setup last night. Everything seemed fine until I checked on them today. The res has dropped 2″ and all 4 pot trays contain the same amount of water. The same medium is used for all and each has the recommended amount of washed gravel at the bottom then the two layers of root control material then medium. The plants are already very well rooted as they are a month or so old and came from fabric containers which gave them very strong root foundation. The res is one foot of the floor. A standard 4 pot setup with two per side. The two pots furthest from the res have noticeably damp medium where as two that are closest to the res are very dry. The trays all have water in. They haven’t started to show serious signs of under watering yet however it is starting as the bottom leaves are turning yellow. Can anyone please advise me as to how to resolve this matter? I greatly appreciate your time and assistance. Thank you