When playing with the curve, set and note the initial timing. Also note the spring combination in the distributor. Increase the engine speed, and note the speed at which the curve begins along with the speed at which the curve ends (where the curve is "all in"). You can also graph the results by checking the timing at 200-rpm intervals (correlating the advance shown on the harmonic damper to the engine speed). Test the results and begin again. Trial and error plays a major role in the selection of a proper curve. What you have to obtain is good throttle response along with detonation-free timing.
As mentioned earlier, some engines will "like" more initial timing than others, while some combinations will want more total timing. In any case, you can adjust where the advance starts, the rate of advance (slope), as well as the total amount of advance. It will take some time to sort through the timing maze; just be certain that you record all changes. Those notes will be a valuable guide when setting up the curve for your particular combination.