Well, as full disclosure, the elastic effect is not fully understood. Those coefficients came from some statistical analyses (which I don't have a ton of knowledge about). I do seem to remember there being a new season post a few seasons ago saying that the elastic effect would now have a small effect across ALL skills. Looking at the trainee above, that would make his IS train faster. It also said that it would still be linked to related skills, so that would make his Passing train faster.
There was a post a long time ago from JosephKa (user who made Coach Parrot) that argued that the elastic effect is shared across skills that train the same (for example, Passing would be lifted by Handling and Driving). It seems to make sense based on rumor, but I don't think the BBs will ever fully confirm how it all really works