I was told many years ago it was due to the panhard bar location (by Land Rover) however that hasn't really changed since the RRC so I don't really believe that. I think it has more to do with the front timing cover design/filter angle over the years. I wheel the heck out of my LR's and I've never had the larger filter ever make contact with any suspension/steering and a larger filter area is always better than a smaller one.

The PH16 is the same size filter used on the Jeep 4.0L I6. When I had my 05 Rubicon back in the day I immediately noticed it was using the same size filter as the D1/D2 and on it's first oil change I did myself up until I sold it I installed the larger PH8A (Mobil1 M301 or K&N 3001) oil filter. I never went back to the smaller filter.