Monster Battles - only two. Am I doing something wrong?

I've never had more than 2. Even after waking up the next morning. After the time I was away for about 16 hours. 2 every time.

OK so I woke up to 4 this morning, but yesterday was 2.. We shall see what the day brings. Maybe it is random?

I'm thinking maybe it's based on how long you wait between fights. After my fight finished yesterday it was just 2 at a time for the rest of the day. This morning I had 8 and 6 in my towns...the town with 8 fights had one of the yellow worms that allow 2 to fight it so basically a total of 9 possible fights with only 5 characters that can fight at a time.

I had the yellow monster twice already!!! and yes it allows to place a second fighter to fight along with the first one. Unfortunately I clicked so quickly I only placed one fighter and it was both times ugh so crazy. I hope I get them soon again.