I don’t see a picture of my molds, but they are completely open in the back and are about 1.2 cm wide (from receiver end to the outer corner). They each have a tiny hole (about 1mm in diameter) for venting.
The problem I had with my first ear mold fitting was that the ear molds were not completely to my canal shape, were letting in sound causing “harmonics” (that’s what I was told) and painful voices in quiet environments. I was refitted for a second set of ear molds, but the fitting was done differently. The second time it was done with my mouth wide open while the impression was done. That enabled a more accurate fitting and no further “air leaks”.
I do have venting in my ear molds. I have no “occlusion effect” (sounding like under water), nor do I have any feedback or chirps.
When you complain of “feedback chirps” that sounds as if you have air leaks around your ear molds and not a tight fit.
Every type of dome that I previously tried before being fitted with ear molds allowed chirping and feedback issues. That just about drove me insane so I know what you’re going through!