I’m almost done with my 20” Grendel and I did a 4.5-18 FDE LRTS. I’d do the same, or a 3-12, on an 18” just because cartridge can stretch its legs on a longer range. Coyote hunting, an offset red dot all the way for close range sneaky pete’s.
My Grendel is a deer gun and I don’t plan to need...