A.N.S.A. as an instructor in zn area environment I would not allow a trainee to let two a/c at, or crossing, levels to remain on own navigation. As an examiner, I would stop the checkout.
Many years ago, when NDBs and Fan Markers were still common on Airways, I was taught to intercept the centre line at an angle of 30 degrees when given own navigation, then proceed to the next RP. I suppose many of my generation would still do this unless specifically cleared direct.