No. The 0.5 comes from the range which is 500 yards.I think i get the math he did, just subbed .5 for .6 to make the math a little quicker. Where is the +/- .3 coming from? and where did you get 5th bracket from?
Well if you want a center hit then it would be half the size. However if you just want a hit, hold the upwind edge of plate and you have a few more mph of wind (budget) to play with. But the right answer is half the width for a center hit.Although thinking about it now should the error budget be the full width of a given target size or half of it?