This is a fair point. The flat part of the tread must be vertically below the arch, or it falls foul of 'the rules'
I know this from my years as a 'blue forum' member. That's why a lot of modified cars ran stretched tyres, to achieve 'poke' without breaking the rules.
Of course, this all is a moot point as an individual officer can make a call 'in their opinion' and it is up to the motorist then to prove innocence. That can get messy. Trust me, I ended up with 3 points and a fine many years ago for having no battery clamp - long before it became an MOT item.
On a positive note, the Discovery looks awesome, and as long as you don't drive like a dick, you shouldn't* have any issues.
*Not a lawyer.