One thing you forgot to factor in is the choice of Intimidate/Reason/Charm adding between -1 and +1 to the roll, this changes the scorecard slightly:
1/2: Impossible for a starting player
3: 3-5 wins required
4: 2-4 wins required
5: 2-3 wins required
6-8: 2 wins required
9/10: 1 or 2 wins required
11+: 1 win required
Obviously it may be possible somewhere that -2/+2 becomes available though I've not seen it personally. This'd make only 7 irrelevant, which be a far cry from the massive range you quoted out of context.
What I do find funny, however, is how often the opponent will not throw the same symbol twice if the symbol just lost, to prevent you throwing double rock to beat double scissors.
