I think what sentinel is trying to explain is that Training Speed is affected by a number of things, including:
• Age
• Height
• Training regime
• Elastic effect skills relative level
The 1v1 guards and wingmen is the same exact training regime as far as we know, therefore whether you train at PG or at SF is the result is the same.
Height is connected to the training regime. Taller players train faster in inside skills and slower in outside skills. The opposite is true for short players. If you want to train a 5'9'' player as C, you can, it will take a lot of effort and it will be very slow. Some skills train at about the same speed irrespective of height (if I remember correctly in 1v1 and even passing the drop in speed is quite low).
Age has an effect across all training regimes, the higher the age the lower the speed proportionally for all regimes.
Elastic effect is the effect skills you are not training directly have on other skills. For example IS has an impact on ID. If IS is much higher than ID, ID will train faster.