Vertical Freedom, check your math...
You say the Astar is burning 20% per hour above 10,000 MSL, I'll take your word for it, never having operated the aircraft that high.
But 6% isn't 33 minutes at that rate; it's 18 minutes. 9% at that rate is 27 minutes.
They say flying at high altitudes may impair math computations. Fly safely.