I have a similar setup ( Ultegra 11speed ) and successfully put a 11-36 SRAM cassette on for hilly rides. Just needed to tighten the b screw to get the jockey wheel to clear the cassette. This may not be low enough for you though.
Are you able to lower the FD sufficiently to work with a smaller chainset. I believe there are compatibility issues using an MTB FD with road shifters, so sticking to a road FD is best .
I have a similar setup ( Ultegra 11speed ) and successfully put a 11-36 SRAM cassette on for hilly rides. Just needed to tighten the b screw to get the jockey wheel to clear the cassette. This may not be low enough for you though.
Are you able to lower the FD sufficiently to work with a smaller chainset. I believe there are compatibility issues using an MTB FD with road shifters, so sticking to a road FD is best .