FLAC has a clear/unique understanding about the used channel numbers and channel layout, see https://xiph.org/flac/format.html:
With the current implementation based on the amlogic and the S905X within the Vero3, four channels pairs are available for PCM: FL+FR, FC+LFE, SL+SR, RL+RR.
Unfortunately only the following layouts can be configured with that
amount channels = 2, PCM 2.0 or 2/0.0 ↔ FL+FR
amount channels = 4, PCM 3.1 or 3/0.1 ↔ FL+FR+FC+LFE
amount channels = 6, PCM 5.1 or 3/2.1 ↔ FL+FR+FC+LFE+SL+SR
amount channels = 8, PCM 7.1 or 3/4.1 ↔ FL+FR+FC+LFE+SL+SR+RL+RR
all other combinations “in between” have to be mapped to the next “higher” layout like PCM 4.0 which can be 3/1.0 or 2/2.0 will land to PCM 5.1 and so on. Again, there are combinations possible where “empty/silent” channels are used but the situation improved a t lot from the previous implementation to map all to 8 channel PCM and the current refined solution to have 4 most common used layouts for PCM. The common audio layouts within video material are all covered with that.