I agree with James that your FS Voltage Threshold is very conservative.
I also run on 3s batteries and I try to get back to the ground (land) by the time the battery is 80% discharged. I have done quite a bit of research on this and I understand if you stay in the range of 80% discharge your battery life is significantly longer. I have done quite a few tests and for my batteries (SLS) it seems that 10.5V as threshold does the trick. When yi fly until FS kicks in, by the time the copter has landed the battery is typically at 80-85% used, so exactly where I want to be...
After several flights in this mode I now know exactly how many minutes I can stay up before the battery is "empty" so i even can land just in time manually and don't need to rely on FS saving me
Hope this helps,