My experience with staining developers, and I've used a lot of them, is that for the most part they contain way too much stain. Even if there's no fog stain a developer like PMK can have unmanageable contrast from all that stain. I wouldn't worry about trying to increase proportional stain at all.

I use ABC pyro with a strong acid stop and Ilford Hypam fixer. I still get what I consider to be too much stain (sometimes). Image stain seems to be a very inconsistent thing.