Hmmmm, that doesn't sound right.
I've got OEM red and black coils (bought from VW and Audi dealers respectively, not internet parts) and they poke into the plug holes exactly the same. Same 'clink' sound when engaging onto the spark plugs, same length, same materials, same everything - just a different p/n.....which just denotes the colour of the plastic.
One obvious clue of an OEM coil is a squirt of dielectric grease inside the coil connector. Think it's a pale green colour from memory. The pattern coils I've seen don't have that.