Depends on length of hanger and size or ring up front. 1st attempt I managed to get an SS derailleur to 36t with B-limit pushed to max. Other time it barely worked with a 32t.
Needed the Roadlink as was running a 46t up front. Frikking love di2. Plug. Play. Experiment.
I'm running a 6870GS with an 11-40 on a Surly Straggler with no hanger mods. Running 1x, SW-R600 Pave shifter on a flat bar with M985 brakes.