Is there a way to make the tactics trainer progressively more difficult?
Not sure I understand your question since as your rating rises, the questions become more difficult. That said, some of us are less than happy with the time pressure and prefer to mostly train in unrated mode. By going into your settings for TT you can set the problem range for anything you want. Coach Heisman believes strongly that you should master easy tactics problems in the same way that you do the multiplication tables. A lot of us can solve advanced tactics puzzles but we're doing the equivalent of adding 6 to itself 7 times rather than knowing that 6x7=42. Pattern recognition is the buzz word for tactics training and you get that by mastering easier puzzles. I believe Coach says you should have at least an 85% solve rate while doing this. So I have my unrated puzzles set around 200 points lower than my actual TT rating and spend most of my time working them while doing a token rated puzzle or two a day. That's a long answer to a question that I may not have understood in the first place, but then I seem to do that a lot.
EDIT: So in unrated mode I do the puzzles until I'm getting almost all of them right, at least 90% and then I bump the upper limit 10 points and repeat. Eventually some of the puzzles start to repeat themselves so if you've been getting them mostly right it's probably time to set the bar a little higher.