Quoted from pinballinreno:This mantis style protector must lay flush with the playfield surface, Or possibly just a hair above.
Mantis style protectors traditionally would sit slightly below the playfield surface.. hence why they were preferred as interfering less with the hole/shot compared to cliffy style protectors that were 'over the edge'.
The scoop takes damage as the balls bounce off the back of the scoop and on games like AFM.. from balls coming in from the side angles and hitting the opposite edge of the hole. You don't need the protector above or flush with the PF. The thickness of the metal itself allows it to sit that dimension under the edge and still prevent a hit against the edge of the PF.