I've had this happen before.
Basically any time you have a custom PMG model as an XML you need to tinker with a few things.
First off, find a pmg2mqo and mqo2pmg converters; run the PMG through both of those in that order. For some reason no matter what you do to ego glow positioning, it will not work until you do this step.
Next, open your [weaponname]_ego.xml file. Your job now is to get what ever effect you want in the position you want. An easy way is to load your PMG into Metaseq and find the coordinates that way.
I've gone through a similar dilemna so I somewhat know what's going on. If you have an account on MU you can do searches for the topic/guide.