I am not sure I fully understand the issue but will take a stab.
First there is movement phase, then comes Patrol/Intercept movement. Reactionary movement occurs in our games during the same impulse but right after regular movement. It is after all in "response" to someone else's movement not concurrent with it.
Our campaign rules say that a PI (reactionary movement) occurs in response to a move not parallel with it. So if someone moves next to you (into sensor range) on impulse 1,... then you have the option to enter that hex the same impulse but right after them by executing the PI, thereby triggering a battle on impulse 1 of the turn.
It also states that it you must close the distance in using a PI (similar to the Drone following rule of SFB), you cannot choose to move parallel. It is not free movement anywhere.
In our games scouts "see" two hexes and the PI covers quite the area then and they can guide the fleet they are stacked with, so Scouts kick ass !
Note:
In our current game the PI rule has a slight experimental change that we are looking at the ramifications of.
We are allowing the reaction movement to also be to run away. So if a single FF is on PI and it sees a 3 ship fleet move into sensor range one hex away, the Patrol/Intercept can also be used to high tail it away into any of the 3 hexes opposite where the attacker is. We used to make you plot either PI or FB (fall back) Now we are examining the combining of the two into a more flexable move for the players. So far for this campaign, it is getting good reviews and working well.
The one area of movement that causes a chuckle in our crew is when two fleets are right next to each other and both plot to move at each other and attack. What hex is the battle in? We decided long ago that it is random, and now a days, use our online die roll generator to find out