# of chapels is SO deceiving however.
Some chapels have 30 parishioners, others have 3,000 or more (St. Marys KS).
As you pointed out, FSSP gets full churches that can hold many hundreds -- so the question is, How full do they manage to pack these churches on Sunday?
SSPX sometimes, due to cheapness/re-allocating resources to build "monuments" and other reasons, often chooses to have 2 or even 3 Masses at an overcrowded chapel, rather than upgrade. Along the same lines, the SSPX will often MERGE two or more chapels together, so they can sell the "excess" real estate because they are greedy for money. They are greedy for real estate too, but only because it can be sold for money. Not so it can be used to save souls. Not unless the saving of souls ALSO gives them money and power.