Wow. Well spotted! :clap:
According to Bowey, Parsons & Parsons, Bagley Glass, p. 131, "Other companies made similar posy vases but the Bagley one can be recognised by its wavy ridges on the outside underneath the wide rim." In the pictures on the same page, the ripples go right to the edge, and the height of the wave (peak to trough) under the rim seems to be greater than on the Belgian one. (The Bagley one seems to have more ripples as well).
I had no idea that the lookalikes were so similar. Without the mark, it would have fooled me for sure, and I'll have to go back and check what I thought was my Bagley elf.