A question about fit. As I noted when I got my K 10s the fit is the best I had in CIEMs. Now I notice the following though which I did not pay attention to earlier. When listening while in bed laying on my back or in park etc. there is loss of seal in that I can notice a decrease in bass and reduced fullness in the sound. If I push them I can hear the sound come back but as soon as I let go it is back to sub-optimal. As soon as I sit straight or get up I get a good seal back.
Is this normal or should I be trying to get a tighter/more snug fit?
I don't know how JM views this topic, but there's always a certain degree of compromise with CIEM fit.
Some people's ear canals change shape more than other people's, in various positions. That's not a cop-out; it's a well known thing that humanbeings do not all have identical anatomy.
When you lie on your back, your jaw slides backwards a little, due to gravity, and this can influence the shape of the ear canal.
If you are someone whose ear canal changes shape quite a lot in different bodily positions, then there will be a greater chance of slightly losing seal in certain bodily positions. I myself find I lose seal a bit when I lie on my back, although I am fortunate that I do not completely lose it, just a bit.
Unless you are one of the fortunate people whose ear canals change only very minimally with different jaw positions, then you would need to have CIEMs that are quite uncomfortably tight in order to be sure of never losing seal in different positions.
Such is life.