In order to stay on the rollers you have to be able to steer, the further the front roller is in front of the axle the more difficult it will be to steer. 3" is not so far as to be a likely problem but it probably won't help all that much either. I learned to ride by putting the rollers next to a wall and bumped off the wall with my shoulder til the balance trick was learned. Once you have this worked out move the roller so it is just below the axle.
Steve