As esshup menitoned - ""You can get more to spawn in a given area if the males that are protecting the eggs cannot see other close males. i.e. you can get more to breed in a smaller area.""
Pallets will produce more FHM spawning areas if there is an additional divider or wall inside the pallet. Currently pallets have one 2X4 in the middle. An additional 2X4 or similar divider to make the space between the middle and center wall not as wide will allow more spawning of FHM due to their territorial instinct.
In a confined space if you bundle short pipes together this gives FHM males confined spaces to create territories. Example - See page 1 in the Q&A Structure Archive ewest's post dated 29/07/07
time 1:06pm on his pictures 9 and 10 for groups or bundles of pipes.
https://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=92463#Post92463
