The question is interesting, but Yurii is right: you must give more information in order to get concrete answers.
It is important to know how did you (or the work you refer to) compute H+ transport. Also, if it is in water solvent or not is critical since the transport mechanism can be very different, and so the value itself.
I am interested in this. Please, provide more details.
Let me make one guess: is the computed value(s) you refer to much smaller than the experimental one?