It’s also worth looking at the exit route for the cable and outer at the shifter end. Not too familiar with 105 10 speed but with Dura Ace there are 2 possible routes you can choose. thread the inner through the outer at the shifter end, put the outer into the cable stops and hold tight to the loose cable. Shift through the gear and feel how much friction there is simply in that one piece of outer casing, it may surprise you. Either try the alternative route (if there is one) or look for ways of reducing the drag on the cable where it enters the outer casing in the shifter.
Hope that makes sense!