I definitely would consider addressing the T in the drain line also. IMO, that is asking for trouble later on and also reduces the amount that can flow through both drains.That’s what I’m seeing, and that’s what I will try is to shorten the drain pipes some. I also tee’d the secondary drain into the primary just above the sump, wondering if that may also be playing a part.
I will be running a bean animal overflow on my 60 cube and will run a dedicated 1" line for every leg of each drain.
Here is a dirty pic of my overflow box. (Tank has been sitting in the garage uncovered for a year while I gather equipment/parts slowly). Haven't cut the emergency drain standpipe or build the durso secondary drain yet.