Hey I've been curious about this. I have been thinking about moving my seat back a couple of inches or so and thought I might add the MBL risers under my Helibars to compensate. However, I have mine set in nearly the lowest position and the throttle cable is already quite taut. I'm not sure I'll have enough slack to put them in their lowest position if I move them back farther.
Have you checked yours to see if you have the full range of positions since the risers?
Jason