The smallest chainring that normally fits on a Sigeyi MTB power meter is a 32T round or a 34T oval. This is because if the chainring has a lower tooth count than the two listed, its overall diameter could be smaller than the power meter itself. This would potentially cause the chain to rub on the power meter.
However, in some cases, you can run a chainring as small as a 30T round or 32T oval chainring on a Sigeyi MTB power meter.
Specifically, if the chainring in question has an offset built into the chainring holes (see the image below), it should work with a Sigeyi. For example, many 30T round and 32T oval chainrings have extra chainring material around the bolt holes. This works to create a small space (usually about 1 mm) between the power meter and the chainring. This allows the chain to sit properly on the chairing and not make contact with the power meter. All our 30T round and 32T oval Sigeyi MTB chainrings have this offset built into them.