Fuel flow, scalars and the MS Nav Log

I have recently modified fuel burn performance parameters on a 767 to about half of what the original model called for (which was burning fuel over twice the rate of an actual 767 in similar conditions). I did this by adjusting the scalar in the cfg file for that aircraft. Test flights show that the scalar adjustment was effective, reducing fuel flow by about 60% (I can now fly trans-Atlantic!). The problem I now have is that the Nav Log shows the innaccurate estimated fuel burn from before I made the adjustment to the cfg file. Is there another parameter I need to adjust somewhere to bring the Nav Log in line with aircraft performance?