How much time before a ModeS plane transit over 3 receivers the receivers have to be in sync? I often see synced with 4 receivers but no positions are computed…
And furthermore has the ADSB traffic to be the same on all receivers o a receiver just need an adsb traffic to sync with?
In that case, there is a group of 3 receivers available to do mlat. (That’s not enough for results - you need 4).
Each receiver reports only the directly synchronized receivers on the stats page, so in your first scenario (a with b and b with c) A will report 1 synchronized, B will report 2 synchronized, C will report 1 synchronized.