Mixing valve in multizone radiant heating - connect to its own return or joint return is fine?

Hello


There are two schemas here - 3 zone radiant heat with mixing valves for each zone. At first both looked to me equivalent, but are they really? Can points "A" and "B" be swapped, i.e. so that the zone 3 instead of taking cold water from "its own" return line (left picture) first joins its own return with the rest of the zones and then taking that (right picture)?

Maybe it's a naive thinking, but for the right side picture my worry is that zone 3 might be taking water from two zones on the left whereas its own return will be going straight to the tank, so the two pictures are NOT equivalent and in some situations right picture can produce wrong results.

More generic question, can I join all returns from all zones first and then feed joint return to each zone mixing valve instead of feeding each zone return to its mixing valve first and then joining after (first two zones on both pictures)?

Thank you