"He who marches out of step hears another drum." ~ Ken Kesey
I don't think longer initial exposure is the right way to go, complete exposure maybe, but you should be trying for that with plastisol too. We block out DC screens with emulsion and expose that after it dries, which gives the washed out stencil a post exposure anyways.
I think we do pretty good with complete exposure on our plastisol screens... and always post expose, usually in the sun for 20-30 minutes... blocking out with a 2nd coat of emulsion sounds interesting. I assume you're just blocking out the edges, or are you doing a thin coat over everything that's not where your stencil is?-JPS. Still waiting to see how others do with the UV LED units... would rather not invest in a MH unit if the LED stuff works out well.