In order to get the reach measurement right, do I need to add to the effective top tube length due to the set-back seat post?
You do not use saddle for and aft position to get correct reach to bars. You use it to get preferred knee over pedal position. Then if reach is not right, you change stems within reason or get another bike that is the right size.
Thats what i did.Seat is right but my reach is short,looking down behind front hub so went from a 90mm to a 110mm{about 3/4 of an inch} stem.Now i most likly need longer brake cables and housings but not a biggie.