I do pot-in-pot with 1:1 ratio of water to brown rice. We have a number of small stainless steel bowls that we set on top of the wire trivet (don't forget a small amount of water in the main pot too). I cook for ~15 minutes for most brown rice and then let the instant pot sit undisturbed for another 10-15 minutes while the pressure naturally releases, and the rice has a chance to take up any unabsorbed water.

White rice is the same deal, though I usually go a few minutes less (~12 minutes). I like to add a very small amount of some sort of oil to the inner pot with the rice.