In the past I also did some split grade tests. But afterwards i decided to first get my negatives 100% and that i understand measuring light. I got a developer for life (my own created pyrocat) and when I finished all that, it almost had no problems with printing these on grade 2. Sure split grade can help you a little more on that point, but it will not save a ruined negative... I do not want to say that your negs are no good, but want to say that the picture depends on a lot more than only the last phase. So try to adjust all the parameters to the best values, and stick to that.
keep on the good work!