I had custom silicone molds made by ReSound so that I could wear my Omnia 962s (size 13 battery) with M&RIE receivers. The molds are rather large, but they work very well to control feedback and to enhance bass by not letting it escape my ears when streaming. IIRC, a Costco HCP told me that their molds are also made by the respective HA OEM. I had my molds made with Select-A-Vent and am currently using a no-hole vent plug. I don’t mind the occlusion, and I really enjoy being able to block low-frequency noise as well as possible - less of a concern with your greater low-frequency loss.
Your loss seems a bit outside the fitting range of the M&RIE receivers at 2 kHz. I’m very happy with the Omnias equipped with the M&RIE receivers. I’m entering day 9 running on my initial set of 13 batteries and hope to make it to 2 weeks!