Yes: closed domes do sound occluded. The open domes are a way of venting the aids - not unlike the vent holes in ITE-style aids (those with a hard plastic shell).
I like your description of the tulip dome. I had also tried them out on my Oticon Opn miniRITE aids for a few weeks, but due to my hearing loss, found they were TOO vented.
It’s a process! I had also tried out foam domes that I bought at Amazon.com. They were SUPER comfy, but I couldn’t seem to get a proper seal, therefore could not hear on the phone AT ALL.
When at the audiologist’s yesterday, I brought a picture of a “zip tip” - which I’d read about right here on the forum. My aud-guy said he’d fit one patient who had an allergic reaction to the material used. So, that nixed THAT option.
I now have double-domes, size L, which seem to offer comfort, some breathability and still a good seal for better hearing.