I see. It makes sense that more chemical goes in between the layers. But it does not make sens in some other ways. The 25xx tanks are larger. The the outer edge of the reels rotate at a faster speed than the inner layers. So the outer layers of film receives faster flow rate of chemicals than the section in the middle. The difference can be large if you load long film, such as 2 rolls of 120. In essence, you get different agitation rates.
Since the film tanks should be rotated at a lower rate, it should not be a concern on the chemical getting in between the layers. I'm more concerned with the different agitation rate.
I already have the 1501 reels, so I do not think I'm going to upgrade to 2502 until I hear something different.