Sorry but no. Military leaders are issued Terms of Reference that define their area of responsibility. TORs always close with a catch-all that says "and other orders as directed" but that's an AND statement not an INSTEAD OF statement. Those "other orders" must be accomplished in addition to the primary direction being provided to the officer. In Dowding's case, his primary responsibility was air defence of the UK, hence why he refused to send more fighters to France (air defence of France was France's problem to solve, not Dowding's).
Your suggestion to pull back north of London would be an abrogation of Dowding's responsibility to defend the UK. No military leader ignores their primary mission on the off-chance of some future "what if" possibility. You fight tonight with the forces that you have - you don't hold back and wait just in case. Holding back and waiting cedes the initiative to the adversary, and you risk having your forces picked off.
Not sure where you're going with the Tirpitz thing but its only real contribution was as a resource sink for the Allied bombing effort. It represented a potential threat that had to be neutralized. FC, or at least 11 Group's defensive area, still had to be neutralized regardless of where the aircraft were located.
You can't guarantee that FC would remain intact. That is a MASSIVE assumption that isn't borne out by the facts of air combat. You have yet to answer how FC will defend its airfields north of London if the Luftwaffe takes out a sizeable chunk of CH? Again, look at Poland, the Low Countries and France where, without radar, airfields were incredibly vulnerable. How could FC protect its airfields if it doesn't know German attacks are even coming their way? The Observer Corps might be of some use but the amount of warning they could provide would be minimal. There's a real risk that much of FC would get caught on the ground or still be struggling to climb to height when the Luftwaffe arrived overhead. That's not a recipe for a winning strategy. It's very likely that FC would suffer greater losses than was the case in the BoB as it played out.