The flaw in thinking additional external aux ATF coolers will impede the engine coolant radiator...it does not or enough to reduce the main radiators function
If so, then remove the AC condenser (the tube fin radiator in front of the engine coolant radiator) and the OEM external aux ATF cooler, which are all in front of the engine coolant radiator. That will remove all blockages this line of thinking would require for proper functioning
Sizing by the thermal dynamic systems designer/engineer has the main coolant radiator good for the maximum conditions spelled out in the specifications. Plus whatever MAXIMUM margin management allowed (always too low to suit me...like lots of margin, but bean counter's penny-pinching wins).
That sizing then has a throttle to no over cool the coolant and is the thermostat/etc.
IMO, if the OP wants to keep their ATF cooler, sure thing, add either a larger plate ATF cooler in place of the OEM...or add another plate type cooler plumbed either in series or parallel to the OEM cooler. Key to keep the OEM routing that has the ATF go through the OEM radiator, which will keep the ATF at proper temps in extremely cold climate conditions
Fastidiousness is key in working with ATF plumbing.