Hello Jennifer:
Are you using any sort of medium that contains a metal drying agent in it perchance?
If so, then the whole fat over lean concept is, to my mind, much less of an issue. Mind you, you will still want to pain fairly thin in your underpaint as you have stated you do.
Most metal dryers will blister over the paint and cure from the outside in, whereas lead will dry more evenly through the layer.
Regardless, keep your layers fairly thin and you should be just fine.
