Once you ad a vocalist, using stereo techniques on the guitar becomes problematic when a vocal mic is added into the mix. This will result in comb filtering due to differences in arrival time at the different mics.
So when recording acoustic guitar and vocals at the same time, another solution is needed.
With very clear demonstrations, Marcel uses two figure of 8 mics to get a great result.

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marcel van limbeek, recording, acoustic guitar, masterclass, vocal recording, recording vocal, neumann u67, Schoeps CMC6, MS, recording vocal and guitar, phase, comb-filtering, omni, cardiod, figure of 8, fig 8, spill, reducing spill