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Cool Breeze, this is a really good question and it's frustrating that belt makers don't provide precise measurements of the stiff part. I shift it to the left, but I still want my buckle to remain between my front belt loops. For best performance, I've found that I want the belt to be tightened within 1" of minimum. Especially with the Zero Heavy, which is really not very stiff.
I wear 31" pants. My actual dimension through belt loops is: 33 (tight) -35 (with holster).
I bought a 32" Heavy belt. The non-stiffened part was 10" long, and the stiff part is 33". I cut off excess to leave 6.75 non-stiffened and re-sealed the tip with epoxy.
I still have a love/hate relationship with the Heavy. The buckle is the only thing that makes me want to use it. It's genius. The strap sucks. It's not stiff, but is super thick.