In the player thoughts message low could mean 0 or up to 5 or 6. Your sf will get improvement in that range for lp, and somewhere in the 7-19 or 20 range in all other cats if you give him the minutes.
BillyG touched on this, but something I've often wondered about is how can a player come up as average in FSS, and then high in the player thoughts message? I had a player get scouted as average in bh, I immediately gave him minutes and he was listed as high in the player thoughts message. I get the feeling that the fss and player thoughts are slightly different in what they list as low, avg and high. Honestly, I think it should be, since one is your asst coach who sees them play consistantly, the other is a national player scouting service.