Personally, I think that the hour to crash ratio is going to be inversely proportional to age, I'm 38 an have to go to work to provide for others so my crash / hour ratio is lower to yours.
If you are 18 (and heal fast) your crash / hour ratio could be higher.
I did an 2 hour plus ride today, Lost balance a couple of times but didn't crash. I should have tried harder I guess.