LOL, nice description Chris.
Just remember, the key is that the enemy Diplomat has to be the ONLY enemy that you have LOS to.
Your opponent's whole team may be able to see the Diplomat, but as long as none of them can see your piece that is shooting, then you are OK.
Hmmm.....perhaps some pictures would help?
OK, in this first one, the Stormtrooper can target the Caamasi (shown by green line) because the Stormtrooper does not have LOS to ANY of the Rebel troopers (shown by red lines). Notice, that all of the Rebel Troopers do have LOS to the Caamasi, so you can see how that doesn't factor into the situation.
Again, the Stormtrooper does not have LOS to any of the Rebel Troopers, so he can still target the Caamasi.
In this last example, the two upper Stormtroopers both have LOS to at least one Rebel Trooper (shown by the green lines), so therefore, they cannot target the Caamasi (red lines). The lower trooper does not have LOS to any of the Rebel Troopers (red lines), so therefore, he can target the Caamasi.
I know the red/green lines can be a bit messy, but hopefully that helps.