Black and White scanning 48bit RGB or 16bit Gray?

I’m scanning Black and white negs with Vuescan and Nikon Coolscan V.
Am I right in thinking I should still scan at 48bit RGB RAW dng, I’m sure I saw that in the documentation somewhere?
However I have tried scanning to 16 bit Gray RAW dng and converting in Neg Lab Pro and the results look identical, but I have a file a third of the size.
What should I be doing.