and as you hit a higher rank there are fewer milestones to get, so if you're rank 12 and 0% you only have two milestones to hit, both of which still keep you at rank 12

if you get under 337,500 honor at this point, your rank doesnt move at all
if you get between 337,500 and 500k honor, you only get to the 337k milestone worth of progression
and anything after 500k is wasted