So, just as a update, I've taken multiple whacks at this via the unreal editor, but have not met with success.
The closest I have gotten is finding the tree for when you have more mechs then slots that procs the choice of which mech to send to storage.
Couldn't find a single line of data that looked like it could be modified to increase the number of active storage slots.
I think it may actually be a "physical" asset somewhere in the files, rather then a relatively simple code line.