Thought I'd reply to this, 'cos I just got the fixed loop for my P-01 holster.
My unstiffened Wilderness belt fits fine; snug in a good way.
My stiffened (polymer lined) Wilderness belt barely makes it through, because of the velcro section. It was sized for OWB or 1911 IWB, so it's too short anyway.
My 1.5" Monica Kuehn cow leather gunbelt is as snug as it could be and still function. You can’t even shake the holster off. I wouldn't use this day-in, day-out without either asking Tony to make me larger loops, or buying a new, slimmer belt.
My Volund belt is precisely 1.5” wide and 3/16” thick, but it has additional loops and velcro for the g-hook system. The tip of the belt fits through fine. The sections with velcro and loops don’t fit through at all; you'd need pliers to get them back out. (DAMHIK)
I can use my Volund belt if I rig things just right so that my holster sits at the end of the belt before it connects to the other end, which is what I'm doing right now.
The split kydex loops are noticeably more rigid than the soft loops. Obviously with a stiff belt it's much less convenient to take the holster off.