How to - Dont show parts on the minimap ?

I have unreachable eye-candy places in my map and i want them to not be displayed in the minimap...

i tried the official tram map and there are unreachable structures outside of observation (behind window),
but its not displayed on the minimap. i checked the groups (especially CommanderInvisible) but i cant figure out how to "not render" parts
on the minimap, inside the minimap-extend.

how do i do this ?