When I have a 4 star or a 3 star player how many times should he get 2x SA addition when we train him with the 15% sets to determine if he is a fast trainer?

From just guessing I would say maybe 4 star every 5-6 times the 15% he should get 2 points, 3 star maybe every 3-4 times.

On my second team Level 25 I am searching for a second fast trainer DC and I can't find anyone. I have a 18 yo 74% GK (so basically 94% for Level 24) who is 109.0 M value which means there has to be 109 M 4 star players in my level, but they are rare. I also have a 18 yo DC 85% with 109.4 M who also should be a fast trainer. My assumption is that every 4% the 18 yo players get around 0.1 M market value. So the DC should be even a bit better than the GK.

The only others I found are a 18 yo DC 44% with 108.1 M, which should be not so good and a 18 yo DC 69% with 108.6 M value, also around the same speed of training assuming the numbers with 0.1 M per 4% gain are correct.

Have you any experience with these values going up in my kind of levels, so the twenties, where we get + 1M market value approximately every 2 seasons Nik?