I'd be interested to see what other guys think, but I feel like some of the highly experienced skiers (a lot of which are on this forum) can get away with starting closer to their toughest passes. Using @Horton as an example he has probably run 32' hundreds, if not thousands, of times. He has years and years of muscle memory in that pass. It is a no brainer for him. On the contrary a guy who may have a similar PB (I'm guessing into 39'), but not run nearly as many passes over the years might want to start at 28'...?...?
Personally I'm actually trying to cut back on my number of passes. I ran a set in a tournament this year from a 32/15 opener into 36/35 (7 passes)....I guess I was trying to get my entry fee back in gas used! I've only been course skiing for 3 years and I still sometimes feel like I need those early passes. I now typically only do it for my 1st set of a 3 round tourney, and then start a little shorter for the other 2.
FWIW...I'm now shooting for my 4th or 5th pass to be my toughest....