I raised the possibility of a difference between the 75/4.5 as delivered in shutter and as delivered in barrel because a couple of people, some, IIRC, here, insisted vehemently that theirs in shutter covered 2x3. Mine in barrel, like yours, absolutely positively didn't cover.
This may come down to the difference beween illuminating a format and putting good image in the corners. Some people think that fuzz in the corners is ok.
My approach when testing coverage has always been to focus the centre of the image on the house on the hill opposite me, about half a mile away. Then, assuming the corners are illuminated, first with a 7x loupe I check that the corners are sharp, and after that I peer through the corners of a clipped GG to see if there is mechanical vignetting, and if there is, whether it will disappear at a 'reasonable' usable aperture.
I was a while ago that I tested the 75mm Tominons, and I can't remember whether they illuminated the corners on 6x9 or not, but that would have been the testing procedure I would have used so whether they illuminated or not, it would have been the maximum
sharp coverage that I wrote down in my 'little black book' as being 6x7.
I see that for the 127mm Ysaron, also for the Polaroid MP-3, I wrote:
Just covers Half Plate (not 5x7) needs stopping down for edge sharpness. At 1:1 on 10x8, free of mechanical vignetting at f22.
Whereas for the 75mm Tominons I noted that it covered 6x7 at infinity and wrote no more. That's because I will ocassionally use the Ysaron at infinity (I don't own an Ysarex), but the 75mm I only use in its intended 1.5x-4x macro range - at which point it covers 4x5 with no problems.
In other words - I think you're probably right.
Peter