Ordinary infantry requires 5 models per rank.
Gutrot has a 40 mm base.
Gutrot in a unit with 20mm bases will take the spot of exactly 4 models, meaning the first two rows will only need 3 other infantry models per row to fill their ranks.
Monstrous infantry however require 3 models per rank.
Gutrot has the same base size as, for example, a chaos troll.
In a unit of 5 trolls and Gutrot, with Gutrot in the first row, do you 2 ranks? Because you don't actually have 3 monstrous infantry in the first rank, you have two monstrous infantry and an infantry, who happens to be on a monstrous infantry sized base. I'm having a difficult time figuring out how the rules handle this strange situation.