I'm a male weighing in at 300 lbs and 5' 9".
I've never had any problems with any positions - any issues are mainly psychological. I've worried in the past when ex's have wanted me on top - Ive been busy panicking "if I squish her... how on earth will I explain it to her family"
Most positions aren't a problem, from time to time, doggy can be difficult, but that's mainly because I have short legs... my partners have always had longer legs... I considered getting a copy of the yellow pages to kneel on (tee hee hee).
If this inch for 30lbs is true... well... i think it'll an interesting experiment.