Thank you bartgrp for sharing those details. Great post.
I am now with my senior apple care guy working on this for over 10 months. I left a lot of posts here regarding developments and progress. And recently had to undergo some new testing and making calling log-files and sending them to apple engineering and all. It seems to be a very persistent and nasty technical problem. No clue why it takes so long to fix it, and having more and more people annoyed over their user experience with iPhone 7 and now iPhone 8 too as I understand from your post, even worse with iPhone 8.
Every important message posted here with new angles or info, that I get an update from via email, I forward to my senior apple care guy. I recommend others to do the same when they are in direct contact via email with an apple care guy or lady. Keep everybody informed about our findings. Just forward it to your apple care contact and type FYI on top. Hardly an effort, but good to know that the apple care guys and ladies are constantly reminded and informed.
Your information about iPhone 8 is very valuable at this point, because I was already informed that no guarantees were or could be given regarding this problem for iPhone 8 ... but I did not saw it confirmed or discussed anywhere, till now via your post. Thank you for that. And thank you for your effort of visualizing the problem as well with the image.
The problem can also be explained as when you are calling and you would be tapped on your other shoulder, that you will turn your head in that direction while holding the top part of the phone to your head/ear. It's just such a little movement that already causes the phone/mic totally drop. Every time. And that is quite a normal situation, a head move like that while talking and looking around (for example during walking or looking through documents while talking with someone).
I am keeping my fingers crossed for iPhone X that I am interested in (also because I curently have an Apple vendor-lock at my house and office, it's all Apple stuff), but I better wait for people to confirm it is not having this same issue.
Thanks again bartgrp for your great post. I already forwarded it to my senior apple care guy, who is really working hard to get it solved for me and users in general. But it's a persistant and nasty technical problem ... it seems to be.