User blog comment:Kitahara/Recording drum expedition success rates/@comment-25730832-20150405133137/@comment-25730832-20150411115125

This will be a crazy hypothesis but I'm also considering an inverse relationship between Drum amount and Sparkle ship.

That is, as drum amount increases the rate of GSc per sparkling ship decreases and vice versa.

But that sounds crazy and your idea sounds a lot smoother.

Overload penalty for drum sounds plausible too. During my data collection for 9 drums it leans more toward Normal Succes for a while before stabilizing later on (that might be the luck factor).