The top of the mag pouches should be very close to the top of your belt/pants. This works best with a real gunbelt and a bit of extra room in the pants.
{digging for picture}
OK, this is a small picture, but you can see the belt clips, and they're somewhat adjustable up and down. Tension screws in the middle are also adjustable.
I actually ended up replacing my Tucker Kydex clips with CrossBreed springsteel clips, but most of my holsters' hardware is a grab-bag these days, I simply like the spring steel clips low profile and minimal snagging.
I use one of the Tucker units as a singlestack mag carrier, the CrossBreed version (Kydex shells on a leather backer) for doublestack.
You set the mag tension (by screw or minor heating/bending with Kydex) so the mags are just barely snug in the pouches when NOT on your belt, then when you wear the thing your belt provides more retention. Much like an IWB holster for a pistol, in fact.
If you're not feeling like Tactical Tommy on any given day, the rear mag pouch can hold a small light, or a knife
Sometimes for laughs, I'll slip my NAA mini revolver in there (it's a perfect fit in a 1911 mag pouch)