Hi Geriatric, welcome to the club. I've not taken that plug appart, but just went out to look. Not sure but I think it may have something to do with the little thin flap on the top rear of the green socket part. It's hard to get into without slackening the seat off first to gain more access.
Are they new covers to protect the originals, or the originals themselves that you're adjusting?
As for the important part.... what model/colour do you have and where do you live? Just it doesn't say in your profile.

Thanks reply. They are protective covers and in order to fix them tightly it really has to be done with the seats out.
Even with the six nuts holding the seat to the rails removed and the seat lifted off the airbag wiring restricts much movement. I have a lot of experience but cannot work out how to disconnect this connector.
I must update profile . I live in Portugal and have the 107Trendy 2 Tronic in electric blue.
The rusty drive shafts, castings including brake drums and discs was a bit of a downer three weeks ago when I took delivery and took off the wheels. Have looked under a dozen new Aygos C1s 107s and these parts are rusty on all of them. Manufacturers brush it off as "cosmetic" but I do not know of any other new cars delivered in this rusty condition.
Have just seen iang1966s reply which sounds encouraging.