I wasn't completely sure what Impessa's notation meant, but I thought characters could get the original +2 bonus for 5, +1 at 10, 15, and 20, then +2 at 25, +1 at 30, 35, 40...etc.
The original synergy bonuses remain in place, but there's another +1 at every intermediate 5. Or else, 15 and 35...