So instead of chomping about 13% out of our GCDs it chomps about 6% out (when hitting from the front). Bear in mind GCDs are ~60% of total ideal DPS, so let's say you randomly miss about one in four positionals, that comes out to (40+60·(1-0.06/4))/(40+60·(1-0.13/4))=1.0107 improvement over patch 4.05.

I don't know how many positionals people are actually missing (and of course SE was waiting on the numbers themselves), but if it's more often than that, 1%-2% sounds about right.