For instance: I do not have a fully g5 engineered ship so I can't keep a speed advantage in all circumstances and that opens up possibilities for the NPCs to flip&reverse on me. Also I am not in a wing nor are my weapons engineered so I can't boil them up in one or two passes.
I don't think the flip&reverse is coded explicitly into the behaviour of the NPCs. Here's my working theory on their behaviour (in 1v1). Their rule #1 seems to be to keep range to target at X meters and point the nose at the target to fire weapons and keep position using thrusters in all directions (where distance X seems to vary with ship type, e.g. Adders get very close, Vipers keep more distance). So if you approach the NPC it thrusts away along the line of sight to maintain range while trying to keep aim. If you approach in their forward hemisphere they start to reverse (often side slipping too, see smoke trails). If a player gets too close or lands too many hits (ship type dependent probably) the NPCs reposition by thrusting closely past their attacker (often using boost but not always). After passing they revert to rule #1 again. The higher their rank the more aggressively they use thrusters (pips!) and FA-off to turn tightly and quickly after a pass. If they have engineered thrusters (Deadly, Elite always have) they can turn very quickly and tightly and it becomes a flip. That's also why lower ranked ones fly a normal turn if you get behind them while higher ranked ones often manage a sort of 'turn and flip' and get their nose pointed at you again (unless you boost behind them or destroy them in time).
Depending on how the engagement progresses (shields down, damage) they perform special actions like: ramming, crazy last ditch manoeuvre, running away, high-waking (rare), etc. For the rest their combat skills revolve around managing weapon groups, pips, SCBs, chaff, etc.
I don't think there is something magical (or cheating) going on. It's the result of relatively simple rules, but still annoying.
Joining the discussion a few days later.
Tonight I took a mission to kill 28 pirates. A friend took a similar mission, same system, same target faction, and we went to a High intensity RES.
He was in a Python, me in a Vulture.
My Vulture was a multi-purpose build : un-modded, equipped with 2 pulse lasers, military armor, bi-weave shield, a 16t cargo rack, SRV bay, fuel scoop, FSD interdictor.
My flying style is : FA-on most of the time (my aim sucks without it), FA-off in turns, heavy use of "up" and "down" thrusters to strafe the ennemies, and a lot of throttle and boost adjustements in order to have max agility whenever possible.
I'm ranked Elite in combat, if this information has any value.
I must say that tonight the NPCs used the reverski A LOT.
Probaly 70-80% of my targets used it, for a very noticeable amount of time (so they were not just "drifting away").
The targets ranged from an Eagle to an Anaconda, including the DBS, DBE, Viper MK3 & 4, FDL, Vulture, Dropship, Assault Ship, Asp Explorer and Adder.
Some of the listed ships didn't use the reverski maneuver every time.
The ships that didn't use it at all are the Sidewinder (maybe he didn't have time), Asp Scout and the Cobra MK3 & 4.
I don't know if it is triggered by player tactic or player ship, my friend in the python seemed to experience it a bit less : his ennemies seemed to prefer dogfighting and stayed in a turning-and-boosting-and-turning maneuver loop.
Maybe the NPCs base their decision on the agility rating of the player ship ?
For me as I said, it was almost every target.
It can be a very efficient tactic, but depending on the ship, it's a bit odd to see the NPCs do the reverski as a primary go-to maneuver.
While the Anaconda had a smart idea to counter my agility advantage, for the Eagle it was spelling DEATH in big underlined red letters, because there is no way he could out-tank a Vulture.
Then again, the Vulture is a good ship and as a result, the engagements where not insanely hard. I only lost shields twice, and both times it was against Deadly FDLs with railguns.
But I have to admit, it makes some ships trickier to engage, and it's a real pain in the butt to counter against a decently mobile ship.
I'll try with a different ship in a different system.