why do most builders relocate the grey coil; and does it matter where they move it to ?

Road

most relocate so they have no issues for clearence when using a bell crank throttle set-up, or when using a waterpump the lower pulse line from the carb manifold tends to interfere, and lastly alot do it for looks, most relocate to above the pull starter with a special bracket mounted to the coil mount.

I moved mine off that above bracket. I added a 2 water-outlet.The outlets were right in the way of that coil. They also make a coil bracket that bolts to the pull starter.