Although 135cm won't be far off the mark, any specific dimension without reference to the many other variables will be at best a "generic" answer. You'll be in - or close to - the sweetspot, and for some guys that might be all they want/need.
With each size/model board, we position the mast track so that the middle/centre/50% position is the typical "sweetspot" for that board, so banging the foot right in the middle and starting from there is a very practical way to go. And usually the next settings come from a little personal tuning (trial + error) multiplied by a little theory.
(Slightly further forward for choppier conditions, bigger sails, early planing.. slightly back for flatter water, smaller sails, higher top end speed)
If you really want to understand the finer points of tuning, any specific setting needs to be related to (primarily) sail size, wind and water conditions - as well as the actual board in question (assume ST126), plus minor influences of things like rider weight, straps positioning, sailing style etc.
That's also a slightly generic answer, but I hope you get the idea
Cheers ~ Ian