Multiband Compressors are used generally when you cannot fix something in the mix. If you need to use a multiband compressor, then there is usually something wrong with your mix.
Odus, there are no right or wrong settings for this. You listen to the song being mastered in tuned room and then your ears will tell you what needs to be done. If I need to use a multiband compressor, I will ask the client to fix what ever the problem is in the mix.
Multiband comps are not generally used in mastering Odus. its wide misunderstanding that they are, but until you understand what they do, then you'll understand why there not used.
CJ