Sorry, It doesn't make sense to me, But I am not a sparky.
3.4 or 3.6Kw is neither here or there. 200w is negligible here. 2.5mm is fine. for EACH appliance. 3.6KW plus what ever your 2nd oven is (13A?) is over what 2.5mm can carry (16+13A). I think 2.5mm is about 23A, Without 'diversity'. you...