How far is too far? Coil location

I think the most important thing to consider with ign coil mounting is...heat. The windings are made of copper, one of the best conductors of heat. Mounting the coil on the engine is about the WORST thing you can do for maximising spark energy. Might be convenient, but it cooks the coil, wire resistance increases & coil output falls off.
High tension lead resistance due to length is of secondary [ pardon the pun ] consideration.
An in depth test done by CT magazine tested about ten HT leads of different resistances to measure HP loss. The winning leads [ highest HP ] did NOT have the lowest res leads!