Retail model kits of The Millennium Falcon:

The MPC/Ertl Star Wars version with 3 landing Gear Bays

The FineMolds Empire/Jedi 5 landing gear version

I dont know the explanation why Han & Chewie decided to add another 2 landing gears to the underside of The Falcon, but the set builders who were under pressure to build a whole free-standing for filming in Hoth's Echo Base & on the Landing Platform of Bespin, knew they wouldn't get away with filming tricks they had used when filming Star Wars.

The Falcon docked in Mos Esley & on the Death Star was built against a wall for support:

The Half-Falcon also had support disguised as pipes or in the middle of barrels:

The filming models were then adjusted to match up with the new 5 landing gear set version