Hi,
Can you be more precise ?
On what cube have you created your agregate ? Standard (business content) or custom one ?
How the agrregate is built. What characteristics it contain ?
Did you use expert mode while creating it ? If yes - it's possible that it works very fast despite low valuation. Some of my aggregates that are low valuated works very fast (I used expert mode while creating it).
Regards, Leszek