Is not even

If the baseboard is glued to a wide gap, then it is attached to the wide side, in the same way glue plinths, if the wallpaper enters the ceiling. If the surface is not even, then this is not scary, the skirting board will still stick normally, the main thing is enough glue. Also if you glue the baseboard with a wide side to the ceiling, this visually increases the space of the room.