[Christ]

While the spark plug washers don't offset compression enough to worry about, they DO offset compression, period. Then again, just moving your plugs around to get the proper torque offsets compression... and just RUNNING your engine offsets compression for each stroke... so maybe we shouldn't worry about such small, inconsequential things?

When indexing spark plugs, the rule is generally to point the plugs toward the intake valves on plug-in-center engines, and toward the exhaust valves on plug-on-side engines.

I wonder where to put them on a Wankel?

I doubt knife-edging a spark plug would do much, but I have heard of gains from "clipping" the plugs for high RPM use. (removing the part of the electrode after the bend, and gapping the plug from the side of the one sparkey thing to the inside of what's left of the electrode.)

Generally, just measuring your cylinder depth through the spark plug hole at TDC and getting a plug that is 1/2 that depth will also be beneficial, since they're not always set up that way from the OEM.

Checking/setting gap based on your engine, not your owner's manual... when's the last time your owner's manual was experiencing high-speed glazing?