they rely on having a bulky miners with the plus version than anything else, look at the s5+ as an example, which is more efficient only because there is downvolt...
the only + that has been out that has been bulky is the s5+ .... s3+ was the exact same size and s4+ was slightly smaller then the regular s4
with bulky i mean that it deliver more hash, without having a better efficiency, if not for some downvolting or downclocking, which can be done manually with the non"+" version