When doing an isometric assembly using 3 points, facet etc., do the objects need to be on the same workplane?
3D objects are possibly rarely on the same workplane, unless you are careful to draw every 3d object on the world workplane and then move it.
What problem are you having?
For me, assemble by 3 points is the most useful, though I don't often need all three (one can use, one, two or three). The others, by facet is occasionally useful for quickly moving & rotating an objects facet onto another object, if I'm not bothered where abouts on the facet the object is, (handy for when the facets are angled). edge and point I don't use,