Yeah you get higher iR bonus based on your grid position. So I want to start last, kick it, and prey on mistakes or out drive my other competition in the rear
Nope. Your grid position (if you don't qualify) is directly based on your iRating, but there is no difference to the payout because of where you start.
Made up numbers here for the sake of an example.
-I could qualify, start third and go on to win the race and I'll get +100 iRating.
-I could not qualify, start 12th and go on to win the race and I'll get +100 iRating.
Starting position does not matter, iRating does (remembering that if you don't qualify your starting position is directly related to your iRating).
As several people have said above, all that matters is finishing position. Specifically, yours relative to the people above and below you. The iRating system is a modified ELO system (
http://en.wikipedia.org/wiki/Elo_rating_system). ELO only works for matches with two participants though. So if there are 9 people in your race and you come 5th, iRacing pretends that you lost to the top 4 and beat the bottom 4. It calculates the points won or lost in each "duel", and then sums up to provide your overall points gained or lost.
Strength of field is merely an indicator of the average iRating of the field. It doesn't affect iRating loss or gain directly, as the individual participant's iRatings do that already. What SOF does affect is how many Championship points are given out for the race. A low SOF race will give out zero points for last, and then maybe an additional 2 or 3 points per position above that. A high SOF race could give out 6, 8, or more points per position. Finishing as a midfielder in a high SOF race can be more lucrative in terms of points than a win in a low SOF race.
This is why it's important to have a feel for the strength of field, and not push too far beyond your own pace. Wins are not always possible, and by pushing for an unattainable goal you're cheating yourself out of championship points if you crash. The goal for the season is to win or place well in your division, not to thrash the Division 1 guys when they show up. Unless you're in D1 I guess...
While we're at it, any iRating movement of less than 10 points is basically zero. Your iRating will fluctuate up and down naturally by about a hundred points or so just depending on whether you're having a good week or a bad week. It's not something to stress about. I'm naturally around about a 1500 I think, and I bounce up and down between about 1400 and 1600. I'm down after the weekend when I get thrashed in the F1 and V8s, and I'm up during the week when I do OK in the Skip and Mustang.