Some rims have fairly shallow channels which makes mounting a tire a challenge when the bead fits deep in the channel. The best fix for this I have found is to replace the rim tape with a high quality plastic HP rim tape, ie Velox, Vittoria or Continental. The plastic rim tape allows the bead to slide easier to the inside of the side wall. When I ran into your problem I tried everything like you; it was only when I replaced the Velox cloth rim tape I had used with some Velox plastic tape that the the tires finally seated correctly. I changed the rim tape and the tires centered themselves and popped into place when I inflated them.