I had to toy with mine to get it just right...it either had stuff coming out of the top or it wouldn't collect anything in the cup....toy with it and you'll get it right. FWIW I had mine pushed down just slightly...maybe an inch.
Took about 2 months to get my BH-300F collection cup perfect. It takes time and if it like mine you might find the sweet spot for it but that doesn't mean that the bubble level will stay there constantly. My bubble level flucuates(spelling) from time to time.