Hell of a thread you guys have going. Don't want to interrupt, but thought you might like a general understanding of the sat location process.
When the satcom transmitter checks in with the satellite, the satellites keep a registration of what the received signal level was. It's obvious that this is all they are going off of now.
When you've got an object moving in the third dimension it will significantly expand the range that you have to consider for the transmitter to be in. What they are doing here is building an area within a received signal level (RSL) threshold where both satellite A and satellite B would be receiving a range of signal levels. For instance, you limit it to an area where sat A receives between -85 to -90db and Sat B receives between -40 to -45 DB. There are lots of other considerations such as interference levels and noise to be considered.
Once you have that area mapped, you have to mirror it across the line of latitude shared by the two satellites in geo. This is because you only have two satellites, and points where similar signal strengths intersect would happen in both places. It's kind of like picking the two spots where the circumference of two circles in a Venn diagram would cross.
Great stuff on this thread.