that's a non-existent semantic difference, as far as I can see.
'how far inside the shell is the mic?'
'it's about half-way in'
seems a totally reasonable response to me.
in fact, I might find "it's about halfway inside" potentially confusing, if I start to over think it.
'inside' almost implies the coma that isn't there, when one HEARS it, rather than reads it.
So if I said out loud that I was 'half way inside the room...' I think it might heard as 'I was half way, inside the room.' begging the question "inside the room, fine, but half way to WHERE, or what?"
I don't do anything by half measures.
But then I speak English English, primarily, with some inevitable American influences.
There are, no doubt, variations
but I still tend to think these two choices are interchangeable, at least in this context.
just like the SM7 and RE20