Military front bumper types?

My son has a military bumper on the front of his Ninety, where the centre pin goes in the back of the bumper is flat.
Seen one where the back of the bumper is round and deeper as if for a bigger towing/trailer eye, what are these bumpers for?
The standard front panel on the Defender would get in the way if fitted to the vehicle.

Like this

Don't worry it will fit, thank goodness.