So, is there something else I haven't done?
The hero's army shouldn't affect it. Most often, the problem is the absence of a castle or enemies, something like that...
Hello! Can you tell me how to change or add a custom starting bonus on a map (not a campaign), besides the three that already exist?
You can add additional effects to the bonuses using scripts, but without a mod, it won't be displayed in the interface when selecting a map.