@Christian_R thank you! This is very, very helpful. The methods you show in the video also work for me, and from the post you linked in your “Add-on,” I found this quote illuminating:
It’s as though Dorico considers the slash and the note (or cue) above it to be like two quarter notes (one stem up, one stem down) occupying the same rhythmic position, and thus offset a bit from each other. And so, this offset is removed/corrected by increasing the distance between them (intervallic-ly in my hypothetical two-quarter-notes example, or graphically in the solutions you suggest).
While I (think I) understand why this behavior is now occurring, it seems to me that this behavior is appropriate for the above two quarter note examples, but in the case of my original vertical slash-alignment issue, I do NOT relish having to manually fix all occasions of this issue. It would be great if this could somehow be corrected globally…