Start Boost % is the new variable and it scales between "Boost Target 0%" and "Boost Target 100%"
If "Boost Target 0%" is 10 psi and "Boost Target 100% is 20psi" then "Start Boost %" of 65% gives you 16.5psi.
See this thread for some example and an actual use of these:
http://www.e90post.com/forums/showthread.php?t=658117
It actually scales between the two.
