Metheg Use in Aleppo and Leningrad

I've been working for almost a year now on the critical apparatus for BHQ Isaiah, and I've noticed an interesting phenomenon. We're using Goshen-Gottstein's HUB version of Isaiah, which is based on Aleppo, as a sort of jumping off point for the critical apparatus. As part of my work I'm in charge of cataloging errors and harmonizing the text with Leningrad, which is the base text for BHQ. The differences (at least in Isaiah) between Aleppo and Leningrad are relatively insignificant, but the vast, vast majority of the variants arise with the use of the metheg. Leningrad seems to use it far more often than Aleppo, although there are also a number of places where Aleppo includes it against Leningrad. Could there be anything significant at the root of this, or is it just the preference of the scribe?