Odd and even 4D56 pistons different?

[Maxedoubt]

I was pleasantly surprised to find some oversized 4D56 pistons on Amayama, but was confused when I noticed that some were notated "1&3" and others "2&4". Then I saw some aftermarket ones on eBay (Tornaumotoren in Germany) that had 1/3 and 2/4 stamped on top. WHAT'S THE DEAL? Are they really different, odd-from-even?
I built a 4D55 some years back, and the ITM slugs I used were all identical (came as a boxed set). Additionally, I've seen 4-piston aftermarket sets for 4D56 with no such markings (all the same). Can somebody straighten me out on this?

[jamesmohare]

The only thing I could guess is something to do with the shape of the underside of the piston to guide the oil jet spray for piston cooling. the oil jets that spray upwards are mounted in pairs, between pistons 1 and 2, and another pair between 3 and 4 and theyre aimed at the center of the piston. This means that pistons 1 and 3 get cooling oil spray from a slightly different angle than pistons 2 and 4. If they also have an arrow indicating which way is the front of the engine, maybe they took this slight angle change into account?

totally a guess, but that was the only memorable thing different between the cylinders from the times ive had it apart (a few years ago now)