Haha my opponent has been doing the same for the last 12 hours. He mimics my narrow diamond so I changed to 3-5-2v then he changes to my strongest formation 4-2-2-2, then I mimic the 4-2-2-2 so he changes to 3n-2w-2-1-2 so I'm going to wait until 5-6 mins before match starts and swap the 4-2-2-2 to narrow diamond.

Try this.

Set your formation out to an obvious formation. One that's easily countered. For example, if your strongest formation is 3-5-2v then set them out to 4-4-2 then hope he changes to the obvious narrow diamond then 5 mins before game change to counter lol.