I'll tell you what I use.
All my cages are in a basement that is 67 - 72 or thereabouts during the cold months. I use RHPs in all my cages, ranging from 24 x 12 x 12 cages to a 67 x 30 x 18 cage. All plastic cages: Neodesha, BARRS, and a Monster Cage.
For the large Neodesha (67 x 30 x 18) I use an 18 x 24" PP RHP. In my 4-footers I use a 12 x 18" RHP in the left rear corner PLUS a small 6 x 12" RHP in the right rear corner.
For my 3-foot slanted Neos I use a 12 x 12" RHP. I also have a 36 x 18 x 12h BARRS cage that uses a 12 x 12" RHP.
In my 24 x 12 x 12 cages I use a 6 x 12" RHP.
In my arboreal GTP cage (26W x 24H x 18D) I use a 9 x 12" RHP.
All cages except the 4 and 6 footers are controlled with proportional thermostats. The large cages do not need them; in the warm months I just turn off the small 6 x 12" RHPs.
Regards,
Bill