Worse sound leakage with fully occluded mould vs power dome: why?

[BeLo]

Background:
Phonak Lumity 90 with medium receivers.
I wear Power Domes in both ears but I have an oddly angled right ear canal which causes that dome to work its way out.
When it does this I get a lot of feedback in enclosed spaces and I have to manually push the dome back in. Even at maximum WhistleBlock levels this still happens.

I have tried ear lock whiskers which don’t work for me and have an acrylic SlimTip mould with full earlock but I I find that very uncomfortable.

To hopefully fix all this I’ve got a silicone slimtip mould.
Both moulds are fully occluded and have the same acoustic code of 132626.

Problem

I’m a DIYer and have run all of the leakage and feedback tests myself. I run each test at least 2 or 3 times to make sure that the results are consistent.

When I first fitted the silicone mould the feedback tests looked really good between 2kHz and 4kHz but were actually worse than the power dome above 5kHz.

The next day with the mould I was plagued by feedback so I ran the feedback tests again and this time the mould was leaking sound above 2.5kHz !!! No matter what I do I don’t seem to be able to reseat it to get back to where I was originally when it was first fitted.

The uncomfortable acrylic mould has very low leakage and was made from the same impression.

Can someone shed some light on what is going on here as I’m really surprised that even when well seated the silicone mould doesn’t seem to perform as well as the dome above 5kHz?

First mould fitting:

Power dome fitting:

Acrylic mould:

What the mould leakage looks like now no matter how much I squish it into my ear:

Both moulds together, not a great photo, the acrylic mould goes deeper into the ear canal:

[firenzel]

Hello @BeLo , i just came across your thread and i think that the issues are because of the “open” acrylic SlimTip mold , where the receivers ar not enclosed in the acrylic itself.
Due to this there is a tiny leak of high frequencies from the receiver housing itself into air and outside the mould. This causing feedback and the feedback manager going strong. Perhaps the acrylic mold itself reflecting the leaking frequences from the receiver housing to the outside, whereas the silicone mould does not so much reflecting.

With enclosed receivers into the mould the sound leakage from the receivers housing would be stopped. See symbolic pictures ( courtesly of @Volusiano )

Mold with receiver sticking outside , non sealed receiver

Some sound is leaking to outside , due to resonating receiver housing

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Enclosed receiver into mold ( courtesly of @Volusiano )

lesser or no sound leakage into outside, due to fully sealed receiver.