I have found that the bigger the number of fish in the group,the less they will fight.
Obviously you need to consider the bio load on the tank and still give the fish enough room.
A few years ago I had 6 thorichthys meeki in a 7 footer. I had 2 males and 4 females. The most dominant male became a real bully to the other meeki and became a real pain.
I decided to try the large group approach and put 20 meeki in there.I must of had around 6 or 7 males.The tank was very peaceful. The meeki spawned without any issues.Sometimes I would have several pairs breeding away at the same time.The fish would display at one another and puff their gills out,but there was never any serious fighting.
if your tank is 4 foot x 2 foot a group of around 8 to 12 would be a good number. Ideally you want more females than males, say 3 males the rest female.
It may sound like a lot.We are used to hearing about keeping c/a cichlids in pairs.This does not apply to all c/a cichlids.Some live in groups or colonies in the wild and if tank space allows, do well like it in captivity.
Only the males will get to 6 inches body length the females will remain smaller so a group of about 10 should be nice for your tank.
I have found Thorichthys helleri to be the most peaceful of the ones I have kept.
Thorichthys maculipinnis I have found to be the most aggressive. Thorichthys meeki fall somewhere in-between but are rarely that much trouble.
If you decide to try the group approach I would advise you keep them as the only cichlids in the tank.
Thorichthys tend to come off badly if other cichlids decide to pick on them.They are not well equipped for self defence and can end up with damaged and dislocated mouths.
Ideal tank mates would be livebearers, these would also be found together in the wild.
Some thorichthys like different conditions to others some like very cool well oxygenated water and are sensitive to nitrates. Others like thorichthys meeki are hardier and like it a bit warmer.It is a good idea to do your homework before you choose which thorichthys species you want to keep.
They do make fascinating cichlids to keep especially in groups.
Good luck with your tank if you go down this route.
You won't be disappointed.