I was burning a little time and came across this Weber question. The theory about less ambient noise is logical, but the primary reason that the Weber lateralizes to the worse ear in unilateral conductive losses is due to the Occlusion Effect. In an unoccluded canal, low frequency components of sounds are able to roll naturally out of the canal. However, with an occluded canal, they are not able to do so. Low-frequency tones (such as the 512 Hz tuning fork) carry the volume of signals. If those low frequencies are not able to roll out, then the overall level of the signal is increased. By sticking your finger in your ear, you are containing those low frequencies. Therefore, it is not as much the lessening of ambient noise, but the raising of low frequency components. If there are any concerns about hearing, the wisest thing would be to refer to an Audiologist. Patient report is a much more sensitive tool than any Weber or Rinne ever wanted to be. These questions should be answered in a much more thorough, sophisticated manner than a set of tuning forks can provide.