I would cut the bats to 24-25 inches. 30 inches is going to make an awful squish in a 24 inch space that might actually lose some of the insulation properties in the bats. Also isn't a R30 bat ten inches deep? You want to avoid compressing this stuff.
So, sounds dumb, unless you are resting this stuff down horizontally between the joists in a garage loft-type space where the depth won't matter so much.
Can I call you dumb again? I quite enjoyed that.
Dummy dumb dumbo and his cheap bats. Dummy, dumbnut, blockhead, dimwit, dolt, dullard, dunce, ignoramus, numskull, oaf, simpleton.