Also, opaque white is very difficult to push through fine detail. I usually have to thin it out a bit to get the details to print a little easier. I also find that fine detail gets clogged up very quickly when using water-based, even in the time it takes to load another shirt on. I'll have to press a little harder to clear the ink out of the screen, or make 2 passes. I also keep a spray bottle filled with water handy and spritz the flooded stencil liberally before I load the next shirt. (You did say you were using Water-based inks, right? If not, then DON'T add water!)
This is all assuming that the stencil looks OK. If there's no detail on the stencil, then look into emulsion age, exposure time, and washout. You'd mentioned that you double up your film positives, I used to do that too, but I had a lot of trouble with fine details using this method. It was hard to get everything to overlap exactly right, plus you'll get more light scatter, especially if you're not using a point source.
Hope this helps.
