Oh, now I see how the front brake cable might interfere with the shifter cables.
From Park Tool, an example of crossing over shifter cables along the down tube. I wonder if your internal cables could do this?
In some cases, it is possible to “cross over” the housing, running the front shifter to the right side stop, and the rear shifter to the left side stop. It will then be necessary for the cables to cross back over underneath the downtube. Consider this option, but if the cable ends up rubbing the frame, it is not a good idea. There may be some light rubbing between cables, but this would result in less friction than poorly routed housing.
