Sorry to be dogging your posts here, @Sierra . But I do remember a previous thread somewhere on this forum where there was discussion of how ear canal shape may change or not with mouth/jaw movement and what mold fitting technique worked best/mattered most in such situations. Seems to me, rather than just going ahead and making an experimental impression, etc., that if there were some quick and easy way to evaluate your ear canal shape in various states of mouth openness, that would give you a head-start on deciding what you need to do.
My molds were made by ReSound, presumably using their 16:4 mm philosophy and the outside face of the mold is just even with the interior base of my tragus in each ear. According to ReSound, the mold should go no more than 4 mm past the first second(edited) bend in the ear canal. Pehaps I am misinterpreting the depth of insertion from your diagram above, but it looks like more than 1/2 the length of the mold is inserted beyond the first bend of the ear canal. If your present molds are inserted to such a depth and it’s just a question of in what mouth position your mold should be taken, maybe the difference in relative position of the mold in the ear canal explains a very large part of the difference in mold sound/mold sensation between you and me. I wonder if your provider has something like a foam plug that could be reliably position at different depths in your ear canal and by which you could test the sound effects of opening/closing your mouth, chewing, etc. Or if there is something like a tulip dome or power dome that could be inserted to various depths that would provide a decent mold stand-in. Even if you didn’t get the “full-mold” sound effect, by relative chewing sound, etc., you might be able to gauge at what depth your mold sound problem arises.
I vaguely remember, perhaps from a ReSound impression-making Audiology Online course, that the first bit of your ear canal, running to the first bend, is pretty well-cushioned material, fatty tissue lining, etc. Further on into the ear, the ear canal lining is much closer to the bone or harder tissue structures. If my molds sit “outside” in the more cushy area of the canal and yours are more connected to bony/hard structures further along in the canal, that may be the source of your annoying sound problems. As I’ve pointed out in other posts, perhaps because of the structure of my ear canals, the undulations, the arc helicis lock on the top of the mold, I have zero problems with slippage. Perhaps going for a mold that’s designed to be inserted to a good depth to avoid slippage is just inviting other problems…
Edit_Update: Guess I’m misreading, the ReSound blog post says the 16:4 rule is 4 mm beyond the 2nd bend! At any rate, it might be worth a forum survey: who made your molds and are you happy with the result?! Perhaps just as some folks here brag about HA’s and some OEM’s in their perception are better than others, maybe some mold-making companies (associated with OEM’s or not) are better than others in average customer satisfaction - along with a provider’s impression making skills, etc.
2nd Edit_Update: Further point (and a clarification in my own understanding) is the 16:4 rule applies to EAR CANAL LENGTH THAT IMPRESSION CAPTURES and is not necessarily the length used in making the mold itself, which may be only some smaller fraction of the length used in making the actual mold - which the designers chose from the 3D scan of the impression mold. So in my case, the mold actually made to wear begins near the outside of the ear canal opening and runs 15 to 16 mm into my ear - and so it seems compared to the diagram Sierra offered as OP in this thread, my actual mold is much more in the outer portion of my ear canal, lined with softer tissue.