mounting for Air filter box

Hi Guys,

My Air filter housing keeps slipping out of the 2 rubber grommets at the front. There appears to be a third leg underneath which possibly sits in a hole in the engine bay and is held on by a metal clip?  - but mine keeps slipping out. Is there supposed to be a rubber grommet in this hole underneath? or is there supposed to be something else holding it too?

regards
KP