12 month multiple entry

Hi, I applied for a 24 month multiple entry in 2011, I got it, but I had to leave every 30 days, which was very inconvenient. I was training Tai Chi. Needless to say, I had to get a more suitable one. I asked for 120 days for each stay, maybe this was too much to ask? Is this why I only got 30 days?

I'm still interested in this visa, as I still want to train here. If I apply and ask for 90 days per stay, is it more likely that I will get this? The 30 days just isn't worth it.