We had problems mounting the ELT antenna close to the COM antenna.... Transmitting on certain frequencies on the COM would set the ELT off. We ended up (on Super Cubs) needing a minimum of something like 4 or 5 feet. One of the manufactures (I think of the ELT) has a recommended spacing in the installation paperwork. That is one reason why the antenna for the ELT ended up inside. Also, if you are upside down it doesn't get broken off.
Pete D.