With a Non-FreeFloat Handguard, the front sight is mounted on the barrel, so the shift will be practically nil when using a sling or leaning it on something. Where you will have the shift with the Non-FreeFloat handguards is when you use an optic and you put pressure on the barrel by using a sling or leaning it on something. From 0-100 yards the shift will be minimal at best, unless you crank on the sling for whatever reason.

With a Free-Float Handguard, the only time you will have a shift is when you mount a front BUIS on the Rail.