I'm familiar with the term "form factor" describing the Irms/Idc ratio of a rectifier circuit (including the filter capacitor). In other words, voltage multiply current form factor describes the required transformer VA for a certain W DC output. There can't be an ideal value, because the ratio varies with filter capacitor and transformer winding resistance and leakage inductance. I suppose there's neither an ideal voltage form factor, just a real value for a specific circuit.
In other words, an ideal (better saying optimum) solution may be found for the most important aspect of interest; as lowest cost, highest efficency, minimum space or weight... etc.
For instance, in my case (where I live), my optimum solutions are mostly based on the availability of the components that I can buy (in volume) and by which I can build a reliable circuit for the functions I need.
Thank you, I guess I was indeed confused about the concept of an ideal value. Now its cleared, there is not a single ideal value, just different optimum values for different scenarios!