http://victorspictures.com/img/s12/v174/p2036679250-3.jpg
Look at this picture. I’ve noticed this before, that the graphs of MLAT flights and those of ADS-B are slightly out of phase with respect to each other (most noticeable in the wee hours of the night), with MLAT being a bit later than ADS-B.
The difference looks like it could be about one time zone. What could cause this? One possibility is that ADS-B flights are more likely to occur east of my location, and MLAT flights are more likely to occur west of me (relatively speaking). Other than geographically, what separates the two? Perhaps international flights are more likely to be ADS-B flights. In that case, my receiver being in Austin, Houston, east of me, is more likely to have international flights than between me and, say New Mexico. Is that sufficient to explain the graph?