I have followed this thread with interest. I would like to add my comments. I own an old Alphax Synchromatic that discharges my studio flash before the shutter blades have reached the fully open position. This can be easily observed by looking into the lens while the shutter discharges the flash in a darkened room. As long as I stop this lens down to f/8, this problem is not an exposure issue, but if the lens were left opened to the widest aperture, f/5.6, it would be. I can say with confidence that with this particular shutter, the shutter blades definitely do not have to reach the fully opened position for the flash to discharge.
This old shutter does have both X and M sync settings, but there is no problem with my having used the incorrect setting. If the M setting is used, my flash fully discharges before the shutter even begins to open. This problem of discharging the flash too soon, exists at all shutter speeds including B and T.
It is very easy to see if the shutter has opened when the flash discharges, and theoretically one should also be able to determine if the shutter has closed before completion of the discharge. Just look into the lens as the shutter is tripped, and if you do not see the shutter in both the opened and then closed positions during the brief flash of light, the flash duration is definitely longer than the exposure time. Optimally, one should be able to see the shutter only in the fully opened position.