RWA - The ACARs messages go via any of one 4 (soon to be 7) operation Inmarsat sateliites (plus backups). The SATCOMs is continously tracking the satellite on which the A/C has logged-on.
Inmarsat 3rd generation constellation, four satellites in geostationary orbit.
In that area, two birds cover the place, AOR-E (atlantic east) and AOR-W.
The a/c's antenna is "omnidirectional" (actually hemispheric), there is no tracking.
Transmissions are almost real-time.
In other words, during those four minutes the antenna "saw the sky".