sigh.
If Germany does all the things it can do to help its chances of pulling off a sea lion, and UK does all the things it can do to defend itself, what are the odds that the sea lion will work with the final setup? Go look through the “sea lion in alpha 3 thread” at the harris site and you will find the answer.
With the final setup, sea lion is always a valid threat but it will only actually happen if one side is incompetent. If the axis prepare for a possible sea lion on round 1 and the allies play incompetently, then Germany can take London without losses that are so bad that they lose the game elsewhere. If the allies defend UK properly and the axis go through with it anyway, then they are incompetent and they will lose the game. Those checks and balances have been very carefully thought out.