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Not necessarily. The reason it is always on return on modern boilers is because the pump is on the return. Hence the filling loop and exp vess position.
This entry point, (just like an open vented system where cold feed /expansion pipe enters), creates a neutral point. Between neutral and pump rear is negative, from front of pump through system and back to neutral point is under positive pressure. It will work without doing that of course but your whole system would be under a slight negative pressure and that's best avoided. You need to try and design any system with a positive pressure if possible.
This is theory and there are exceptions to the rule but in general thats the best way
Thank you for explaining it will amend it to behind the pump, other than that anything else you see ?