Older packs in particular (like my Normans) aren't capable of as fine adjustments as many of the newer ones, but that's more a question of the vintage of the equipment. Still, if you're just trying to get a variation of a half stop or less, moving the light closer or farther will have some effect on the quality of the light, but not an enormous effect, so it's not that hard to manage with such a system. I've seen after-market variators that can add 1/5 stop control to an older system, but I think of them as more of a convenience than a necessity.