The teams that qualified for semi-finals (by start-number):
SS: 6, 18, 20, 22, 23, 28, 42, 46, 50, 52 (out of 52)
SSC: 12, 20, 21, 26, 34, 35, 43, 51 (out of 53)
There is only one team in the single digits that qualified (that was Champion Cheer Heat).
Teams that qualified when the starting teams are broken down in thirds:
In SS:
first third: 1
middle third: 5
last third: 4
In SC:
first third: 1
middle third: 5
last third: 4
Just from this data your best bet is to start somewhere in the middle, even though on average you score higher starting later. Maybe I'll have some time later to do the other years and get more detail into this.