Just curious -- has the seating taken on a somewhat "assigned" feel? Like Jim always sits in this corner of the couch, Sue always sits in that chair? Does everybody always gravitate to the same spot each week?
It's a weekly event that has been going on for a couple of years, so I can see how some people have "claimed their spot" and others stay away from Jim's favorite spot because Jim always sits there. (Has Jim ever complained -- "That's my seat?")
I'm wondering if you could maybe change things up a bit in a fun way.*
Like play musical chairs before the show starts and then again 1/2 way through.
Or assign each seat a number, then have guests draw a number before they get comfortable and that's where they sit that night. New numbers drawn every week.
Or make it a rule that nobody sits in the same spot 2 weeks in a row. "Because we're getting set in our ways. This is just to do something different each week."
This is an uncomfortable issue with you. Other than calling a stop to your weekly hosting I think you are well within etiquette rights to change the "usual."
*You said in your OP that this is a fun group and you've already solved 2 problems with a group that you've been hosting for years. That tells me that they would be amenable to a change like this . . . especially if done in a fun, not whiny way.
eta: if anybody complains about your change-up? than you should insist that others take turns hosting 3 times a month. You'll take the 4th week.
On the personal side -- I have my Sheldon seat. I claim it as mine simply because I am able to see the hall to the bedrooms, the front door, the dining room, 1/4 of the kitchen and when the drapes are open, the living room and what is watched on TV, along with a perfect eye's view of the back yard and deck. Yeah. This is the all-seeing MOM's chair.
Frequent guests know this. If an unknowing guest sits in my chair? I'll not say a word and do like you do, OP -- hostess takes the short end.