Looking at the entries in 9mm.json, I see no discernable difference between the M9 magazine and the Kel-Tec PF9 magazine besides weight, volume and capacity. They both possess the MAG_COMPACT tag that the ankle ammo pouch looks for, yet I can use an ankle pouch to stash one but not the other. The list of clothing in which a magazine may be stashed doesn’t even show up for the PF9 mag and I don’t understand why.
Is the PF9 magazine too small for the ankle pouch? Looking at my Ruger LCP, I notice that its magazine also cannot be stored in the ankle pouch, and it also has no “can be stored in” entries.