Maybe I am misunderstanding you but are you saying his 'presence' and 'coming' are two different events?
I said:
The first difference between these two words is that erchomai is a verb; parousia is a noun. Erchomai expresses movement, parousia is an event. And thus, the two words can be used in the same context, such as at Mt 24:36-44. The verbs in the context describing Jesus' "coming" (vss. 37, 42, 44) are all part of the event, his parousia. (vs. 39)
I made a mistake in the above quote. Mt 24:37 uses the term parousia. The NET renders it as "coming." That is why I thought (without checking) that erchomai occurred there. But my point is the same. Erchomai is a verb. It expresses action. Parousia is a noun. An event is a noun, a thing. Since erchomai is a verb it cannot be an event, which is a noun. But erchomai can be something that happens during an event.