OK. I wasn't sure if it was electronics or points. The points distributors have a different curve as they didnt have to worry about losing time in the electronics.

To realy know the curve on yours, you'll probably have to get a couple more rpm and and timing measurements.
Based on your 950 rpm and 2000 rpm measurement, if the distributor curve is similar as the later one, the initial timing is around 13 degrees. Great for easy starting.

I don't think shortening the slots alone will do the trick unless the engine will tolerate starting at 28 degrees. On the graph is a red line showing a more reasonable 22 degrees for starting. If this is what has to be done, then the primary spring will probably also need a slightly higher spring rate. The spring rate will change the slope. More initial tension will shift the curve to the right.