If there is too much venting, the low frequencies just leak out of the ear. It’s not a hearing aid function thing, it’s a physics of sound thing.
Psych also raises a good point. If the “occlusion” someone is experiencing is a muted, muffled sound, this is generally an amplification problem, not an occlusion problem. Occlusion is the chewing, walking, boomy-voice-even-when-the-aids-are-off thing.
All you can really do is try. Confirm with your audiologist what modifications can be done if you get the full mold and find it too bothersome.