I would think he's talking about running with passive wiring to the TIU with 2 PH 180s to a block?
I wouldn't put a 20 amp capability into a TIU channel. Maybe I'm not understanding this correctly?
It was stated that 10 amps is the limit to a single TIU channel? (15 maybe but 20? )
So the OP question is strictly how do they react tied in parallel?