I have no big players that are slow trainers..
is this the scenario ?
no
So far, examining every season from LV1 to LV42 the fast/slow trainers, the only indicator is the higher value.
This rule was very strict, specially in low-mid levels.
But this leads to a conflict with your scenario, meaning that all the tall players with big difference of height - weight should have near max prices.
Which doesn't happening (you can see that in GK where most of them are tall but not all fast trainers).