it seems the user form the quoted post did not insert the extension arms all the way in to their slots, causing the tank to be too high.

but the attached diagram lives no room for error, if only poeple bothered to read the effing manual before they discovered stuff does not work...

even when 1500 tanks are filled beyond MAX capacity in rotation use, the films in any tank longer then 1520 will get more density on one end of the tank.
IE - when loading 5 35mm in 1520+1530 using lift, the films towards the base of the tank (away from the lift) with get less developer agitation resulting in lower density. it is not a consitent thing, but i have seen it range from non issue 1/3 stop to more then -1 stop compared to same type of film in top of tank (closer to lift). this ofcourse refers to BW only. i have not seen this in C-41 or E-6.
the bigger the tank, the greater the density gap between top and bottom. i will admit the biggest 2500 tank i used for film is multi tank 8 (2840) with 8X35mm (and the same with 2X2509 and 18 sheets of 4X5 which i did on a regualr basis for a long time) and i saw no noticeable density change from top to bottom, where as i went up to 10 rolls in 1510+3X1530, and there you can really see the films on the bottom end got less of everything. i tested this on other machines as well with similar, but as i said, not exact consistent results.

who ever runs a commercial lab process (as i did for a while) runs in to these issues. the simple way around it is to make smaller batches.

another thing - the chemical usage difference between 1500 and 2500 is pretty negligible unless you really do a million rolls a day so i take that comment back as irrelevant. however there is about a 30-40% difference between multitank 5 for sheet film and 3010 tanks. (560ml for max 12 plates 55ml per plate - VS 310ml for 10 plates 31ml per plate.)