With my BX1880, I had problems with one side lining up but not the other. With the FEL installed, the bucket (or grapple) would always contact the ground on one side before the other when being lowered. I ended up using a piece of 2X4 on its side under the bucket on the side that contacted the ground first and that is what I had to do every time to line things up for FEL installation.
However, when I replaced the tractor tires, I found that one of the almost new R1 rear tires that were being removed was about a 1/2 inch in diameter smaller than the other. Now with the new tires, I don't have to use the piece of 2X4 anymore when installing the FEL even though the bucket still does not contact the ground evenly, but it is much better though.