M_Boats: boom vang

Hi all, I have a 2004 Montgomery 17 with an 8' boom, which can hang on the backstay in a wild jibe. I consequently tend to run the boom 17" up the mast rather than the 28" that sends the main to the tippy-top. I would be most obliged if someone out there with a similar boat would tell be how high he/she runs the boom, and if a vang keeps the boom from kissing the backstay. It seems logical, but my logic does not always prevail. I am mounting a vang anyway, but I need to know how high to ride the boom so I can figure where to mount the bail for the vang. Thanks ever so much; I would rather be sailing than punching experimental holes in my spars. Tom Jenkins M17 Scintilla