Do you compensate for slides-outs when leveling first?

I guess mine when it does arrive having a slide on each slide won't make too much difference in leveling.
Many of the campsites we frequent are backins and the rears are much lower than the fronts. To heed the warning of keeping the rear tires on the ground because that is where the parking brakes are, do you use ramps on the rear? I understand raising too high can cause the leveler pistons to tweak and then not retract, true?