Might I write my opinion ?
The problems on tactics trainer become more difficult when your tactic's trainer rating becomes higher. When you solve a problem, you can see somwhere your new rating and a + or - and a number, and the problem's rating and a - or +. So these ratings have not a really big difference. Eg, your rating is 1800 and you solve a problem with rating 1775, you are going to gain some points, and the problem is going to lose those points.
Hope I answered your question !
Hi!
I'd like to ask how are the problems for the tactics trainer selected by the computer? Do they become more difficult as your rating gets higer? A staff member would be welcomed to answer :)