What do you think about possibly pulling the two German subs back to SZ 4? First, they wouldn’t have to dodge 2 mine rolls (and Germany has enough to kill Britain’s home fleet anyway). Second, you’re set up to make a joint attack on SZ 8 turn two if Britain should try to drop a fleet. A G1 build of a BB in SZ would help (a battleship could likely survive 2a mine rolls on its way to SZ 8).
I haven’t tried this yet, but it might help a Paris or Bust strategy (preventing British reinforcements to France).