Why do all the backing on? Load the walk behind forward facing first. Then load the zero turn with the casters "straddling" on both sides of the walk behind. I do this without a problem. If I load the zero turn first, I have to load the walk behind sideways.
Ford F350 & Ranger
Exmark Lazer AS 60" 28hp Kawasaki
John Deere GS30
John Deere 14PZ
Honda HRC 216
Shindaiwa T270, M231 Muliti-Tool & EB802 Stihl MS230 CBE