But it also occurred to me that the altar is set up for versus populum celebration. I noted this with my correspondent, who replied oh, no, they celebrate ad orientem from that altar and commented that this makes things rather tight.
But then it occurred to me that an awful lot of OCSP groups are doing things this way, in tiny chapels unsuited to things like ad orientem celebration, with capacities for ;little more than a few dozen -- and unlikely to grow beyond that. Aside from the likelihood that Bp Lopes's estimate of 20,000 non-canonical "members" simply can't be accommodated in venues like this, it's worth recognizing that even when OCSP cheerleaders point to 41 (or whatever) communities, these are the typical places where they meet.
I'd hate to be celebrating ad orientem from those altars with the constant recognition that a backward step could be disastrous.