This is normal variance. I have masternodes that have generated 30 drk each and i have masternodes that have generated 2 drk during the same period. Its variance.
It is simply tough luck.
If you go for Vertoe´s MN service, these variances are balanced out. We just completed the funds for the 50th MN.
Get in before its to late. ;-)
Cheers
Count P