Almost every private tracker has a bonus point system: you are awarded bonus points for seeding (usually non-linearly, where the longer you seed the more points you earn for that torrent per hour) and can exchange them for upload credit.

There's also often various situations where downloading a file costs less for you than the upload credit it gives to others. Most commonly this is via freeleech where a download is not credited (but the corresponding upload credit still is awarded).

I would say that maintaining ratio is not actually a big deal these days in the world of private trackers writ large. These days bandwidth is cheap, storage is (or used to be) cheap, the communities are older and more long term oriented. On many of the best trackers the ratio system is essentially symbolic. RED (from the OP) is a notable exception and one of the only notable trackers where maintaining a ratio actually requires some work--their ratio system is much closer to zero sum.