I don't know what year your Mighty Might is, but here's a link to the 2005 Bowtech Owners manual which features the M.M. http://www.bowtecharchery.com/downloads/2005_OwnersManual.pdf
If you already have that, then I be sorry.
You cannot make significant drawlength changes with the post setting, only very fine ones. Drawlength changes are accomplished by module changes. There are post settings that correspond to which module you've got.
My suggestion though, is to take your bow to a bowtech dealer for the initial setup. S/He might even have the correct modules on hand to get you setup right away. If not,then it's just a couple days wait...