I believe the choice by the founders of AMHR(since they were first, and originally set the standard of where to measure Miniature Horses, which was then emulated by AMHA when it was begun)may be characterized as a compromise, but perhaps not exactly as referred to...(maybe someone who knows for sure will come in with the facts?)--However,from what I have read and heard over the years, I am pretty sure it was a choice made mostly to make the horses 'seem' as short as possible, but without looking TOTALLY ridiculous in the eyes of the horsepeople of the world(i.e., by measuring in the middle of the back....
)!
Although I FULLY SUPPORT a change to measuring ALL Miniatures at the high point of the withers( LIKE THE ENTIRE REST OF THE EQUINE WORLD, for Heaven's sake!!!), I do not consider it all THAT difficult to determine where the last hair of the mane is; IMO, it is best done by using your sense of touch, if in doubt. . When I bodyclip, I don't leave a 'tail' of body hair; but, I realize that it is a tricky business to clip as I do-and would never be critical of those who don't--that said, anytime/for any reason, it is 'hard' to determine mane hair, use your fingertips...there is a DEFINITE difference in the characteristics of mane hair vs body hair(go out and 'practice' feeling of the last, shortest part of the mane over the withers; you'll see what I mean...)
I have NO idea how someone would 'glue' additional hair onto the withers convincingly.(though,sadly, I suppose I shouldn't doubt that it has been and is being, done...all I can say is, I would not for ANYTHING-money, comfortable circumstances, kudos, fame, you name it-- trade places with anyone who 'needs' that badly to cheat ....and I pity such people's horses.
(I am compelled to say that a difference of .25"(1/4") from one measurement to another is not at ALL surprising...Although I am a STICKLER for correct measurement, and do NOT believe that measurement is NEARLY as subjective as many seem to think, that amount of difference, in my opinion and experience, is about as much as a measurement 'should be allowed to' vary, but CAN occur without anything 'deliberate' being done to 'alter' as fair and accurate a height as can be documented.....)
Also--I know of no instructional tape or website(at least, anything "official" on measuring. I do know very well how to measure myself, though-and would be glad to provide a tutorial. Better still, perhaps, would be for someone who has either attended, or even better, CONDUCTED, an 'official' measurement seminar for either registry to spell out what is taught there! Any volunteers?
Margo