Yes one can alter the timing at idle and still not affect the timing you want for max torque. One way is to use manifold vacuum on the advance can. That will result in more timing at idle then using stepped, but when you open it up to WOT the vacuum disappears and the timing will drop to what you have the mechanical advance plus initial set to. Another way is to set the total timing to what you need for max torque with no ping, then adjust the distributor plate to not allow the idle advance to drop down below the number you want at idle. I set my curve to get my total advance at 28 as that is where my highest torque came in. I then welded the distributor plate slots on the LOW side to keep the advance higher at idle speed. I then set the timing to 28 degrees at 3200 RPM, the point at which the mechanical advance was full in, tightened the distributor clamp and let the car idle. The result is 19 initial at idle and 28 total from 3200 rpm al the way to 7000 RPM. I then connected the vacuum can for an additional advance at idle that is controlled by engine vacuum. More advance at cruise and idle and no vacuum advance at WOT.