[Willy Wonka]

No I haven't tried changing the ignition timing from standard 16 BTDC..

It's SOP to set the timing by applying your max boost pressure to the timing capsule. Then set the timing for what you'd like it to be at max boost ( 9˚ btdc for me@ 22lbs of boost and 30# injectors and a extra 36# at 3/4 throttle running regapped bosch 4418 plugs ) The system is rock steady for me. I do how ever use custom wires, with the standard rotor.

Here are some 4418 multi-electrode plug pictures of before and after.
http://www.saabcentral.com/forums/showthread.php?t=42409&highlight=4418

 

[Willy Wonka]

I like that, the 'scientific method'. Alter one variable at a time.

By minimum I mean, I have the side electrodes ( cathodes ) touching the central insulator. The resultant gap is about .028" by sight. It does work under full boost with out a lot of knock, or blowing out the spark.
The spark travels longitudinally and is un obscured.
BTW:
This affect is also used by evenrude outboard's new 2cycle
high performance engines. They have stripes on the outside porcelain
insulators which coincide with the cathode. These stripes must be in a certain orientation for the engine to perform optimally. The devil is in the details.