Thanks everyone for giving me the courage to move Théo's roost ! I did exactly as suggested by @bgmathteach .
.
Edited to add : @BY Bob please let us know how yours roosted tonight !!
And how did it go ? Well, it wasn't a failure but I will have to see how it goes tomorrow. I will quote myself from another thread using my special talent at multiquoteI agree completely with this!
If you are able to move Theo's roost so it is far enough away he can't reach Gaston on his roost, but not a huge amount (like if you are able to slide it, say 1 foot (~ 25-30 cm) further away from Gaston's roost. Not so far that it is like a 'completely new location', but far enough he can't reach Gaston, that will probably work best. If not, just move it, period, and see how things ;shake up' Since it is moveable, you can always move it again if it doesn't work.

I will let you know tomorrow how it goes. Here is a Gastounet crowing tax with his beloved Piou-piou in the background .I moved Théo's roost 30 cm/11 inches away from Gastounet's, so that it's now about 80 cm/31 inches in front. The idea was that they wouldn't be so close to one another.
I was wondering if Gastounet would manage to reach his roost as he gets there by jumping on Théo's roost : the wider distance didn't bother him at all. Then, when Théo and the ex-batts came in, Théo didn't attack Gastounet... but this was due to the fact that Chipie got thrown off her roost by Nougat, one of the ex-batt. Chaos ensued. Chipie was thrown away from every roost, including by Théo. She finally managed to roost next to Merle and Gaston didn't attack her
Edited to add : @BY Bob please let us know how yours roosted tonight !!