Forget it.
1. The fact that YF moved and crunched themselves up in the corner, rather than obstruct those who sat in the zone - is testament to YF being good citizens.
2. YF are an established part of the club and everyone has gone to the trouble of designating YF zones at all of the away matches and at the Rec, it should be no problem for the organisers to [or sanction YF to] put up the sign or the rope or whatever to reserve the area and if people sit there and complain, they can be shown to another part of the ground in as polite a way as possible.
Are you talking about me?