Helix at the moment but I remember the maxcoin pools doing the same thing.
It's actually slightly higher than half but it's consistently about 40% lower than it should...
I'm currently using your latest build with the T2880x24 command on a 780ti.
we could try tinkering a bit with the difficulty target in the cudaminer code (artificially lowering it).
If the pools still accept these shares, you would see a higher hash rate and higher payouts
Christian