In looking at the tool against the stone... musing.. do you use a depth stop jig to insure the length exposed is the same each time?
If so then.... given 2" is exposed now and everything else remains the same wouldn't another stop depth at 2.25" have the tool contact the stone at a new angle...maybe 35-40* rather than 45*? Less exposed... maybe 1.75" would result in an angle more in the 55-60*?
Seems like it would work to me and no need for another full jig; just different depth stops with the degree written on them would place the tip at higher or lower angle to the stone.
All tyranny needs to gain a foothold is for people of good conscience to remain silent. Thomas Jefferson