You would need to take your access point and wave it all around various directions in the space around the microwave. The “leak” could occur in a direction that doesn’t have significant signal. Might be a better test to cook a large bowl of water, while testing your phone (outside the oven) on 2.4ghz … holding it on all sides of the oven to see if any areas degrade the signal. This testing approach isn’t that conclusive.