THE IDEAL BIKE FIT ?
Regarding the question of whether the ideal saddle position exists? Of course: every frame builder, and bicycle manufacturer claims to know the secret.
Obviously the standard frames in bike stores are made for average people. Specialist builders can make custom frames to measure, but often only in steel. Because of the flexibility of working with steel, the dimensions of the bicycle can be adjusted, to suit the rider. This is a great advantage for people with a non-standard physique. But naturally this additional value of a well fitting frame size, applies only to the first purchaser, and not anybody that buys the frame later second hand. If you build yourself a custom frame, or have one built for you, the chances are greater that you will live a happy life with your bike, than if you just take any frame off a frame rack.
Production made bicycles (unlike custom frames) only have limited scope for adjustments, by sliding the handlebars, or the saddle ; for people with average proportions and dimensions, these adjustments deliver no real problems. To fit Aunt Hilda and all and sundry, properly on a bike, it is necessary to adjust the saddle, seatpost, handlebars or stem. The slide-ability of the seat position is often limited ; to no more than 20 or 30 mm of movement. The seat clamps of the majority of seat posts, only allow approximately 20 mm rearward saddle motion (see FIG.1).
There are also seat posts which have the clamp located in the centre of the post ; so the seat is 20 mm further forward, (as shown by the FSA post in FIG.2). Tom Ritchey also sells special seat posts with additional setting options, (see FIG.3), but only special saddles of his own brand will fit these seat posts.
There are only three parts, where the rider's body makes contact with the bike : the saddle, the pedals, and the handlebars. The spatial locations of where the handlebars, saddle and pedals are located, are determined by the actual dimensions of a bicycle. But of course, everything has an influence on each other, and how the rider's body balances on the bike ; if for example the cranks are made 10 mm shorter (such as from 175 mm to 165 mm long), the seat must be raised to accommodate this change.
Interestingly, the bike "fitting" sessions that one goes through at company "X", (with exactly the same frame, and the same rider), yields a different result at company " Y". In short, it is not a reliable, and repeatable real science, but one dependent on human interpretation ; of course each company will say that their competitors are wrong ! Advice is good, but only if it is valuable ; you might say, the more expensive the better.
The limited size selection of carbon frames (often only in S, M, L), particularly can cause problems for larger and smaller riders. Nowadays stems are bolted to the front fork. There are some stems that make a greater angle with the steering tube, so that it isn't necessary to use too many shims to get the correct position. Sometimes a stem can even be reversed (upside-down), which can help some very small riders find the right seat position (especially on time-trial bikes).
About 35 years ago, (when the bike fitting industry started), I had myself measured. As I had suspected, I was not perfectly symmetrical ; my right leg was 4 mm shorter, than my left leg.
Following the procedures of the bike fitting protocol, my pedalling motion was analysed using video, I made a test ride on a dynamo-meter, it revealed that my right knee was "wobbeling". I had never noticed it before, so it was the result of the Bioracer re-adjusted position of the cleats on my shoes. The lower part of my right leg is slightly askew below the knee joint, and that I compensate for this by rotating my right foot outwards, when I pedal. I wasn't happy with this result of the Bioracer consultation, so I changed my position again soon afterwards ; nothing is sacred, especially fitting programmes ! Everyone's body is unique (and constantly changing), so every bike has to be unique too, (and adaptable as well). Every rider has to learn (through trial-and-error) what works for them, and what doesn't !
On the wide web: https://www.globalcyclingnetwork.com/video/bike-setup-tips-for-smaller-cyclists-emmas-bike-fit-guide
The saddle can be personalised too: https://www.youtube.com/watch?v=JWnhcMr79jI
I have created an Excel- App to help with bike fitting, see Download ; it helped some people and if it isn't much use for you, then you haven't lost anything, because it is free.