Flexboss21 to Gridboss connection

I purchased the gridboss and flexboss21. I currently have grid tie solar. I am not planning on ever using the flexboss PV inputs. This should limit current between them to 50A. I want to install the flexboss in my garage and the gridboss by my panels on the opposite side of the house. I currently have a 50 Plug in the garage that has a 70A breaker protecting it. Can I use that line to connect between the two? I would rather not have to run 125 to 150 ft of 2 awg cables. Can I use that line and put a 60A breaker on the smart port of the gridboss where I connect the flexboss? I am under the impression that I won't exceed the 50A at 12kW. Any information or suggestions would be greatly appreciated.