So if I recall correctly your map overlay will have a "ground" and "par" level. So it sounds like you want a layer that the player will be behind but an event will be in front of. No events will ever appear above the "par" level, it's just not intended to do that. However, I believe you can achieve what you want doing this:
- Place the piece of the map you want your character to be under and the event to be over on the "ground" layer
- Place an event that displays the wall piece of the map that your playable character will walk under (put the wall in a "character sprite"; even if it's larger than your 48x48 grid size it will still show up as long as you have your "sprite" template setup correctly) => set the event priority "above characters' & check "through" in the options
- Make the event that will be walking on top of the wall => similarly set the event priority "above characters' & check "through" in the options
This should allow event 3 to walk over event 2, and your player to walk under both. Let me know if there is any confusion with this!