I'm glad this came up because I thought that since I was getting passover that I would have to bid at least as high to not have to pay passover back, but I think you are right. I was a Boeing S/O, but am getting passove for the Bus. So if I bid to the right seat of the 75 I won't have to pay it back because the 75 right seat is hihger than the 72 backseat. I thought I had to bid at least right seat of a widebody (what I was holding) to avoid having to pay it back.
Sometimes its good to be wrong!
FJ