PTR doesn't track PokerStars games below 100nl, I don't know why since Full Tilt games are tracked below 100nl.
How much you open for should depend on a few factors, and there is room for getting creative, but there's not much need to get super creative at microstakes. That said, here are some things to think about:
1. Don't vary pf raises based on your hand strength. Too much of a tipoff.
2. A tighter player is better off opening larger than a looser player. The tighter range is more likely to be ahead than the looser range. A tighter player should probably be using 4x as a standard rather than 3x. In general, 3x at micro I think is a mistake as a default, it's too small, even for a loose player I'd use 3.5x.
3. Position is commonly used to vary raise sizing. One line of thought is to decrease the raise size in positions where opener is likely to be stealing and to increase the raise size i positions where opener is likely to be opening for value. As an example, you might open 4x from ep and mp and 3x from lp and sb. Another line of thought is to reverse the logic and open smaller from ep and larger from later position, since you are trying to discourage the blinds from calling your opens from lp. (I subscribe to the former view fwiw).
4. If you're opening for value (i.e., you're opening say JJ+,AQ+), and you're certain other players at the table will call w worse even if you increase the betsize, by all means increase the betsize. So let's say I've opened three hands consecutively, got callers on all three hands, and took all three pots on the flop w a cbet. Now I get dealt AA - by all means increase your betsize if you think everyone's "he ain't got sh*t" detector is ringing and you'll get callers w a larger betsize.
5. If you're opening in front of a shortstacked player, you may want to decrease your opening betsize, esp if you're in a stealing position. This decreases your exposure if he shoves and you have to fold. Note that it's important to not do this based on the strength of your hand - you want him to make his decision without knowing whether you have 94o or KK.
Having said all that, I don't bother to vary pf raise sizes at limits lower than 25nl (and usually don't bother at 25nl either). Nobody's paying enough attention to make it worthwhile.