I, too, was surprised at how much lead I needed to balance my 360 ailerons.  In fact, I have those lead half-rounds going nearly full-span (two of them, flat surface to flat surface).  But let's stop to think about it.  We need as much "moment" (mass x distance) in front of the hinge line as behind it.  In practice, we have more weight (balance weight) forward of the hinge line than we do behind it (the control surface itself) since the CG of the control surface is generally much further behind the hinge line than the balance weights are forward of it.  This is certainly the case with the ailerons, but less so for the rudder and elevators, since they have those forward overhangs for aerodynamic balance.

For preliminary design purposes, my airplane design group assumes that the balance weights weigh 1.5 times the weight of the control surface alone.

Bottom line -- your balance weights need to be at least as heavy as the control surface, and up to 50% more.

Yup, it's a lot.

- Rob Wolf