Electricity will take the path of least resistance. If the wires are arcing, it's possible that the connectors at the plugs are not in top condition, It's also possible that the plug gap and grounding of the plug to the engine block is not at it's best. Would any of the teflon antiseize products on the plug threads reduce the conductivity? I would also test a slightly smaller plug gap to see it's effect. The available plug wires are rubber coated with a cloth weave on the outside to look like orignal products. Even if the cloth is wet, the rubber should have enough resitance to prevent arcing. 9mm wires have more resistance than 7mm wires. More questions than answers. Forgetting appearance, run the wires without using the metal tube and put separators on the wires to keep them away from each other and any grounding potential.
Bob Engle