Activity Diagrams are 2-dimensional, and the placement (or "ordering") of Parameter symbols on the boundaries of Action symbols - and of ActivityParameterNode symbols on the framed boundary of the Activity context itself - need not be bound in any way by the ordering of the Parameters (arguments) of any related Operation or Behavior. They are completely different ways of thinking!
In MagicDraw SysML Plugin and Magic Cyber-Systems Engineer ® (Cameo Systems Modeler®) you can order Parameters on an Operation or Behavior using the specification dialog; such a 1-dimensional ordering need not have any bearing at all on how you organise the representation of those Parameters as symbols in a 2-dimensional Activity Diagram. None at all.
Dr Darren says:
Take advantage of 2-dimensional SysML and UML diagrams to represent networks and flows as best fits the modelling purpose.
For an example, visit: