I change it up too, if I use the side-lateral machine where the forearms are on the pad, then the hands are tucked, I feel you get a very isolated work out with that. If I do the laterals in the cable cross over machine, then I extend my hands out as far as they will go and the forearms burn like hell. If I am doing dumbbell laterals, then the hands end up somewhere in the midpoint between the 2 forementioned excercises.
Ill cycle through these as an auxilliary group every 2 weeks or so.