First of all, if the racing is 3 wide the entire time, how does that leave room for any passing?... Especially on the outside.
Second, while min/maxrace lp placement and increased ai_squeeze_pcnt values have an affect, it's just not that cut and dried that you'll get the desired results. There is no exact rule on values and lp placement, only generalities. It's strictly trial and error, and interdependent on the track, the track.ini ([ track ] and [ track_ai ] parameters), the quality of the race.lp, and the placement of the min/maxrace lp's to bonafide secondary racing lines and their relative location to the race.lp.
Third, on tracks where you never have to get out of the throttle, the ai change lanes pretty easily. If you use an ai_squeeze_pcnt greater than 1.00, you either won't notice a difference or it'll cause trouble.
The leader is going to try and run the race.lp, even if he takes the lead from an alternate racing line. Any ai looking to pass will jump out of the line following the race.lp. Whether they choose the inside or outside depends on the location of the minrace and maxrace lp's from the race.lp, the space to move to another line, the speed that racing line is capable of producing, and other considerations that I can't think of or don't know about.
The ai can be enticed to move from the race.lp by a greater (than 1.00) ai_squeeze_pcnt value. Too high a value will cause the ai to turn off the track for no reason and to run into walls when the lp's run close to walls (especially at clip points). Higher values also cause the ai to leave the preferred racing line (the race.lp) even when doing so provides no benefit, and will in all probability cause them to lose momentum and fall back.
If forced to, the ai will move to the outside, but to get the ai to pass on the outside, the grip must be greater out there than it is in the middle or the inside. At superspeedway tracks, especially, if the ai can't go as fast or faster on the outside, they will lose momentum and rejoin the main racing line.
The ai ratings are also going to have an effect. It's not so much how fast they'll be, although a poorly rated ai in "aerodynamics" and "engine" will be decidely slower, but it's more on how well they can stay out of trouble. Any ai with less than a minimum 50 rating in "track type" and "chassis" is going to cause problems, at some point, in close racing.
Try JGIR, the original track with this addon http://nrtracks.com/nrtracks_board/index.php?topic=227.0
Run the ai in a race. Start reflap and turn on the race.lp, minrace.lp, maxrace.lp, and the raceline.lp (keystroke r). Watch how the ai shift back and forth from the race.lp to the minrace and maxrace lp's. This should give you an idea how the ai will move about.
You might also look at some of the threads at SimRacingDesign, someone's always asking about similar situations.
This one might help: http://www.simracingdesign.com/nr2003-general-discussion/32471-cars-staying-pack-homestead-09-rr-2.html