I read it as: he picks 25 starting spots in the custom scenario designer a fair distance apart, and then players randomly get 3 of those to start in.
Which you can do using the settings below, but then you lose control over how many armies are in the neutrals.
EDIT: Apparently you cannot have auto distribution within slots, so it looks like you need manual distribution too then.
Edited 2025-10-25 18:18:13