don't you mean treeC?
as far as maximized empowered's order of operations
it is indeed the max +1/2 normally rolled result so will be somewhere between 19 and 27.
you're playing in a weird game. honestly, I didn't know that symbiotic was a template until reading this thread. best of luck to resolving this situation, I don't think I have further rules clarifications that haven't already been mentioned.