Thanks for the responses guys
![Wink ;-)](./images/smilies/icon_e_wink.gif)
@Flip - I noticed this person coming toward me
from the planet/port I was travelling
to, and as this was only the 3rd person I'd actually seen in game (the other two were fleeting & literally a second before I hyperjumped away from a station), I locked onto them purely to see who it was/out of curiosity. They passed me, and then turned around/lined up behind me, then the interdiction happened. there were no NPC's within hundreds of ls.
I made my way to the station, and as I was a few hundred metres from the slot, I noticed the hollow square again, so stopped & turned around, locked on & sure enough it was the same person.
@SJT - Wasn't you mate, you're good
![Wink ;-)](./images/smilies/icon_e_wink.gif)
@Aves Roke - Yep, there does seem to be those '3 tiers' so far as interdictions are concerned, perhaps they relate to the different interdiction modules NPC's have ? For example, I was interdicted by a po-po 'Conda the other night & didn't even have a remote chance of getting away, as soon as the mini-game started he was already two bars from being successful & the escape vector was way out of screen leaving me no chance to avoid.