It's obnoxious currently. It should be no more or less challenging than training any other position. There's nothing special about small forwards, per se.
I think the concept of having to play players out of position to train them is completely unrealistic and a poor game design choice. I've shared this before and the BBs disagree. That being said, a small tweak toward allowing you to train a SF while they actually play as a SF would at least help tilt the training in a better direction, if not be the actual overhaul I think would be more beneficial.
So, can you explain what "a small forward per se" actually is?
The problem here is that since a SF can potentially use both his inside and his outside skill with relative efficiency, he should have all of them and as much as possible. This is not true. As a matter of fact, making the appropriate selection for your SF position accounts for more in game strategy than people realize.
By the way, even with the current training system you can train SFs in ID and OD with them playing at their natural position.
"I don't know half of you half as well as I should like; and I like less than half of you half as well as you deserve."