In regards to training the hardest skills first, on account of penalties like height:
Multiple penalties magnify each other in most models of training speed, such as the coach parrot spreadsheet for example.
An example with age and height:
1 week of ideal training / (.75 for age x .5 for height) = 2.67 weeks of training
+
1 week of ideal training / (1 for age x 1 for height) = 1 week of training
=
3.67 weeks of training (to be equivalent to 2 weeks of 18yo with ideal height)
OR (by switching where the age penalty occurs)
1 week of ideal training / (1 for age x .5 for height) = 2 weeks of training
+
1 week of ideal training / (.75 for age x 1 for height) = 1.33 weeks of training
=
3.33 weeks of training (to be equivalent to 2 weeks of 18yo with ideal height)
The 2nd case accomplishes the same amount of training in a shorter time frame as the penalties are not magnifying each other and are instead offset. If those models where the penalties compound each other are accurate, as far as that principle, then it is better to train, for example, the most penalized skills due to height when the trainee is younger. This benefits the trainee by offsetting those penalties.
Training a small forward for example can be accomplished with any height player as long as you account for this without too much of a difference between that player and a 6'6"-6'8, or whatever preferred height, player. Theres a tremendous difference in what that player will be like during the journey, but the end result will be similar. The right height still benefits, along the same lines as multiplying two groups divided out of ten, i.e. 3x7=21 4x6=24 5x5=25.
Good advice would probably be not to worry too much about this, or the 'elastic effect' as well, as the degree of training being sacrificed is likely not great and it may complicate the value of the trainee as a financial asset, or its game performance, during their development. Along the same lines as just using a lvl4 Trainer instead of worrying about the cost/benefit of higher levels trainers. Instead just wait and see if theres a general rule that develops out of it that applies to your situation, training for cost effectiveness/or to develop a national team player/etc. Finding that shot blocking on your good center can develop from atrocious to prominent in half the time as normal and rushing to do it will probably just make a player you can no longer afford.