An interesting observation, and sketch.
I was (and still am) trying to reconcile it with an image i captured on Jan 08 of this year.
Of course, Beta Mon [ 11 Beta Mon ] has many other names... (common practice with astronomy).
It actually forms two of the Herschel Double Stars...
H-1-010 with is STF-919 BC
and H-2-017 which is STF-919 AB
And then, two (2) of the component stars are SAO-133316 and 133317.
I have both a regular image, and then one taken with a 2x barlow.
Of special interest here is the WDS data, shown at the bottom below.
It shows the components as:
AB Angle 133 Degrees and 7.1 ArcSec separation (measured from top [N} down through the left [E].
AC Angle 125 Degrees and 9.8 ArcSec separation
AD Angle 055 Degrees and 26.6 Arc Sec separation.
Thus, in my image, the upper right of the two bright stars (shown lower left) is the "A" star.
Lower left is the "B" star.
And now insert in the lower right of the image, clearly is showing the "D" star in the correct position.
My image(s) can be viewed here:
In my images, N is up (same as your sketch), but E is to the left.
Edited by dmdouglass, 19 February 2019 - 02:56 PM.