I'm pretty sure that you won't see max timing until right before you shift or upper rpm's. In other words, if it's set for 15 degrees and you floor it, it will advance timing gradually throughout the rpm curve and not just give you 15 degrees immediately. Normally it stair steps to get you to max timing so that knock is minimized. Hopefully that makes sense.

Like everyone else said, there are other factors that will pull back timing as well.

At what rpm are you getting 3-6 degrees?