I took your advice and made spreadsheet with variable boundaries to see how it affects each cell.

The trouble im having now is finding the right balance between spreading the cells evenly while maintaining boundaries that make sense. for example one of the best boundary settings in the spreadsheet yielded rpm boundaries of 1900/2100/2800 and map boundaries of 39/50/65.

Those map boundaries seem ok but only a 200rpm difference between low and mid doesnt seem correct even if it does spread them the best.