The smallest chainring that typically fits on a power2max MTB power meter is a 32T round chainring or a 34T oval. This is because if the chainring is smaller than this, the diameter of the chainring is smaller than that of the power meter, and the chain would effectively lie on top of the power meter itself.
However, in some cases, you can mount a 30T round or 32T oval chainring on a power2max, with a bit of a caveat. Specifically, if the chainring in question has an offset built into the chainring holes, it should work with a power2max. For example, many 30T round and 32T oval chainrings have extra chainring material (see image below) around the bolt holes. This works to create a small space (usually about 1 mm) between the power2max power meter and the chainring, therefore allowing the chain to sit properly on the chairing. All of our 30T round and 32T oval power2max MTB chainrings have this offset built into them and work with power2max MTB power meters.
Please note, this chainring offset means your chainline will move 1 mm inboard. This shouldn’t have a noticeable impact on the operation of your drivetrain but it’s worth making note of.