That test though is only if air superiority hand't been won yet. The whole keypoint and the major part of the German strategy for Seelowe was that air superiority had been achieved over the Channel and the immediate shoreline of Southern England. The misappropiation of the Luftwaffe by Georing, Hitler, and the rest of the German High Command along with the gross underestimation of the RAF's ability to operate (remeber that the battle of France made the Luftwaffe think little of the RAF due to it's lack lustre performance throughout the whole campaign) and the effectiveness of British radar stations. If these factors had been taken into account and a more realistic timetable been established I'm confident that Sealion would have been succeseful but without winning the air campaign a succesful amphious invasion is nearly impossible.