Ok so I can only say what you most likely already know, but you have to get this part right, whether domes or custom molds, it’s critical to get this part right and then have your HAs probably programmed to suit.
Now if you’ve had some custom molds made before that you really liked, then it can definitely be done again, I can’t understand why this isn’t happening, other then the impression is not being done correctly.
Also different manufacturers
(it’s not your audiologist that makes them) have different results, Widex is as good as any others.
So your heading into severe loss, I personally would be trying a different clinic to get those Widex moment fit correctly, domes from Widex should be a good start (Phonak domes fit as well) honestly those deltas are not in anyway helping you hear compared what the moment can offer.
Also a good solution from @Zebras, as those slim tubes are a much smaller diameter, but since you already have the moments, maybe your audiology clinic will swap/change for you?