Where is the bleeder in relation to the piston bore? I would suspect it is now on the bottom. This is a problem as you cannot get all the air out of the caliper.

Although, there are ways to get around this if need be. Non, traditional, but ways nonetheless.

Other than that, there should be no reason to not mount them on the bottom of the axle. You do open them up to possible damage from the inside and bottom, but...whatever works.

Michael