That is actually quite common, sometimes less is faster. You can control the car easier, which allows you to get on the gas at the correct time. The other thing that happens, is the more laps you do the faster you go. I try to run enough laps that I can replicate my time within a few tenths lap after lap, then set the HP so it basically takes a perfect lap to get within a tenth or 2. Needing a really good lap to get close to the target allows you to concentrate on driving the heck out of the car, instead of where do I lift so I don't get a penalty.
A trick I did use in the last series was to note my last split time before the SF line on a really good lap, then keep that in mind, and if I were to be ahead of that split time, I may have to slow down a bit.