You were absolutely correct about my "oopsie" on the position of advances. (I think I'm half asleep). However, I was only in error on the total number of possible advances based on the pivot sector. (Point of entry eliminates one of "my 6," so I've adjusted accordingly).
On the large (Waterfall) map:
If XIX and all but 1 sector were owned by the same guild and all of the T2’s were maxed built (with 3 slots in each), that would be 5x66=330 (increased advances) + 220 (base advances) for a total of 550 advances for XIX. So, yes, you are correct on the increased number of advances but not necessarily correct on the total possible number if it were max build/max slots on all adjacents excepting your entry point to XIX.
On the small (Volcano) map:
Example, Targeted Sector C2S.
C2S + C1, C2T, C3Y, C3X, and C3V are owned by one guild. Sieging guild owns B2T, and sieges C2S. 3 slots each at max build in 5 sectors equals 300 + 220 base advances = 520 total possible advances.
**nudges the napkin dispenser back into the center of table**