Looking at the photo, I agree that the leo neckline looks too low and too wide to use a neckband cut as a straight strip. If you have time, patience and some spare black lycra, could you unpick the existing neckband and replace it with a shaped one? You might have to wing it a bit on the exact size and shape the neckband would need to be. Looking at it, my best guess after a wine or two is that it would end up cut as something between a quarter and a half circle, with the outer edge length being the size of the existing neckline. That shape would sit lower and "flatter" on the neck, but short of raising the actual leo neckline I'm not sure how else you would get a collar to sit properly.