Yep, I found weight loss was pretty much the only thing that would drop my blood pressure. Though it didn't drop linearly like you're describing. From 215lb to 180lbs, it didn't really change much at all. Once I got down below 180lbs, it quickly dropped (from ~150/90 to ~120/80) and stayed there. When I slacked off my good eating habits and went back above 180lbs, blood pressure shot right back up to ~150/90. I'm back down again to about 172lbs and clearly get it now, I have to stay here.