Flashback: How is the score calculated?

I'm playing Flashback on SEGA Megadrive. How is the score calculated?
I completed the game three times by now but my total score was:

First round: 167244
Second round: 162xxx
Third round: 155144

In the second round I died or failed 41 times, in the third round only 20 times, so why is the score of the third round less than that of the second round?
I think in the third round I was quicker than in the second, too... So...