A lot of things contribute to your finding legendaries.
- If your bot can survive MP10, but it takes a long time per pack, this could: 1, cause your gold timer to trip 2, reduce your trash pack kills/hr so that the extra mf and item drops are negated by the lower kill rate.
- Your base MF, is more MF on your gear causing you to lose too much dps or die more than you would without it?
Finally, until the new patch comes out, I believe Act 3 will consistently beat all other acts due purely to mob density
Most every class has something that rewards them for continuing to kill mobs (Barbarians thrive on chaos rune)
Being able to kill more mobs in a shorter period of time (not just due to density, but because you don't have to leave/rejoin games as often) will in theory cause more items to be seen, thus a greater chance of legendary items.
I just recently discovered a build that enabled me to not only survive but with equal speed complete A3 2MP higher than I could before, so this has drastically increased my legend/hr. I'll that here.
Barbarian - Game Guide - Diablo III
Essentially, I'd been using damage mitigation previously (Warcry and Superstition), and after watching approx 24hrs with both builds, I've come to the conclusion that damage delt with life steal and higher HP > damage mitigation with lower dps.
Thanks for reading.
EDIT: Also your choice to pickup certain items, since I cut out iLVL 61/62 weapons and 61/armor my legend/hr count has gone up. In general I find that legendaries have a greater potential to be worth money than 61/62weapons and 61/armor, so by skipping over those I've decreased my pickup time as well as increase the time my char spends farming for gear because his bags don't fill up as quickly.