How the rifle slides after the shot depends on the configuration of the stock.
Benchrest stocks will be flat on the bottom of both ends allowing them to ride straight back on the bags.
Chances are your stock isnt designed that way and if not you will be realligning after each shot.
There will always be a certain ammount of aligning anyway in most cases. It's best to just let the forend
lay on the front bag and keep your non trigger hand on the rear bag to make fine tune adjustments.
A rabbit ear bag is best for that purpose.