Taggify generates a synthetic point tag with a scope of just within the query line. What that means, basically, is that both the taggify expression and the other expression have to be part of the same query line. If you have them split out into 2 query lines, the second query line won't "know" about the synthetic point tag.
BTW, since we may all be in different Wavefront environments, it's probably helpful to post the full queries in addition to providing links.