I have three triple convertible lenses - two B&L Protars and a Rapid Rectilinear probably made by B&L. All of them came to me with the lower length lens on the front and the longer on the rear when combined. For instance the RR has the 20” on the front and the 28” on the rear. All of the B&L catalogs I’ve seen show the longer element as the front element when combined. Which is right, and does it really make any difference?