I looked up the pipistrel virus 121, nice performance chart in section 5.9. Ignore the KTAS, the percentage of power and fuel flow at 2,4,6,8,10,12 thousand feet is what you need. Make your own palm sized card with that data for reference while flying at altitude.
Interesting how the 55% power fuel flow increases fairly dramatically as altitude increases. Carb not totally compensating, rich mixture? And engine speed (increased friction losses) to get required power at altitude.