The range of audio levels coming out of the SQRX on SSB is difficult to match to the FM transmitter. If you recall we've had problems with too strong stations on SSB up causing the FM transmitters to behave poorly and overdeviate. I can only imagine it would be 100 times worse on Field Day. It's a good mode when everyone behaves though!
I guess I've missed those passes you mentioned. The issues I've heard working the cross-mode V/U passes tends to be centered on stations aligning their uplink signals to be heard by the SQRX receiver while compensating for Doppler. Even at 2m, that can be a challenge with an uplink receiver that has filtering to pass - I think - 4 kHz in SSB. Not the same as working FO-29 or HO-68 in SSB with the larger passbands.
It is interesting that an organization like AMSAT, one that is trying to increase membership and raise funds for a new satellite, would try to limit the usefulness of its prime satellite to a few dozen stations (number based on WA4SCA's message from earlier today regarding L/U activity during Field Day last year) during the busiest on-air activity for hams across North America. Yes, V/U may be chaotic, no matter if the uplink mode is FM or SSB for Field Day. Work 20m SSB during Field Day, and that is also chaotic. We don't try to have ARRL rule out using SSB or CW on 20m during that weekend. Even V/U FM on AO-51 is a "good mode when everyone behaves", ;-)
Again, just some thoughts and observations. It is good to see the discussion about something related to satellite operation here on the -BB. 73!
Patrick WD9EWK/VA7EWK http://www.wd9ewk.net/