Sorry, but this makes absolutley no sense to me at all.
If your draw is 28" then it's 28" Why on earth would you want to shorten your drawlenth just to shoot a shorter arrow? How do you get any kind of consistency?
I'm sorry, but the last 1" of your drawlength is where your back tension comes properly into play. If you lose that inch, all you're doing is muscling the bow back which in turn will screw your release.
Drawlength is measured to the back of the bow, so if you're drawing the point flush (How would you know that anyway?) you've shortened your draw to 27" If you're not using consistent back-tension, how do you know when you're at full draw? I know that I can touch my own anchor point at 25", but when I then expand my chest to correctly come to full draw (still touching anchor) my draw increases by 5"! I know when I'm at full draw not because of the arrow length, which is irrelevant, but because I simply cannot expand any further without either moving off my anchor, or releasing the string!
You'd be far, far better served by learning your correct form & then sticking with it, rather than messing around with arrow length & changing your form with every shot.