We have 4 tiu in super powered by 8 postwar ZWs.... Each tiu has 2 zws for power using the a & d handles . One handle to each channel ,( Var set to fixed). However each tiu channel is separated from another with a center rail insulating pin. It seems you don't have any separation between channels.
Although our layout is single track, it could have been 4 separated loops using 2 tiu in super. Hope this give helps a bit. .
Bottom line keep your blocks or channel zones separated by an insulated center rail joint.