How can I tell the arrangement of 5.1 channels?

I am writing a plugin that has {6, 6} configuration (5.1 in and out). The plugin treats each channel individually.

First testing with Logic, I was trying to figure out the arrangement (order, layout) of the channels: whether it is SMPTE (L, R, C, LFE, Ls, Rs), Film (L, C, R, Ls, Rs, LFE) or another.

After much research, the only thing that gave it away was a preference in Logic (Preferences > Display > Mixer > Level Meters) that showed the oblique `Internal (L, R, Ls, Rs, C, LFE)’.

I have no way to be sure such will be the case with other AU hosts, or VST, AAX, RTAS hosts.

I must be missing something truly trivial, but how can I retrieve the input/output channel arrangement?