I have a set system for setting up the position on my bikes and this works for me-But last week I was out on the Tandem and after about 20 miles the saddle hurt. The saddle had been set uo right and for 20 miles was ok. What had happened was that the saddle had slid back about 1" on the rails. There was no way I could ride like this so I lowered the saddle by 1". At least I could now ride without pain, but it did not feel right. (To adjust this saddle on this post was not an option due to not having right tools and it was dark)

Saddle position is very important and takes in Saddle height, fore and aft position and tilt on the nose. It will vary from rider to rider and as I found out, one slight change and that saddle does not work.

By the way, Forearm measurement as a rule of thumb does not work for me whatsoever. On my Kona I am well short and on My bianchi I am well long. Both bikes fit and are comfortable. And don't even think of any rule for the Tandem as that thing throws the rule book out of the window.