It would seem that the only way to determine the effect of different group spacing would be to use an optical bench. I do know that Steve Grimes (RIP) determined by micrometer measurement the spacing of the groups as they were in the barrel and he insured that this same spacing was maintained when he mounted the front and rear elements in the shutter. I assume, therefore, that there must be a good reason. Among those might be coma, spherical aberations etc. Those would not necessarily be readily apparent by viewing the "sharpness" on a ground glass.I have found, in my experience, that lens performance is readily apparent even on a contact print. Obviously the effects would be more noticeable as the degree of enlargement increases.