I'm afraid that won't work. I always have to centre my S8 very precisely, and despite taking care, it always happens that the S8 was then not charged overnight. Covering it with wood not only adds distance but also makes it difficult to centre it correctly. - You can try it with a test setup (wooden plate), but you have to do it for at least a month, because a single test does not show how sensitive the arrangement is (in terms of positioning).