I reckon it might make sense if the spacer color area of an image font wasn't significant in the actual font, I think it would be better if it was like "insignificant whitespace".
It seems like the spacer area is appended as transparent space on the right side of the character, but if you wanted transparent space on the right side of character, you could, y'know, just put transparent space on the right side of the character. :P
(Possibly perhaps maybe kinda somewhat related:
#466. If the spacer color area wasn't significant, 0 pixel spacing would be possible.)