I would hesitate to place emphasis on where a tech lives in the hiring/wages realm. If the applicant is qualified for the position & the position pays x, then that should be the rate offered.

What if 1 area of your territory was more profitable than another because of circumstances out of your tech's control- would that tech be paid accordingly?

You state that this question is to make it fair to all tech's- I applaud you for attempting to do so, but if fairness is the goal, are in shop tech's rates/percs different from one another based on their home address?

I think the real question is how to make it profitable to have a road tech cover an area when he has to travel a greater distance than most to get to that territory. I don't believe the answer to that question should ride on the back of the tech. Perhaps a reshuffle of territories to better cover your area with all your tech's.