I agree with your thoughts on placement. If BRS is used, I plan on manually activating the ELT during descent. If for some reason the airplane overturns, the antenna is then pointed towards the sky.
My replacement ELT is an Artex ELT 345. It is an excellent unit and reasonably priced. It is the standard ELT Phil Lockwood ships on all his AirCam's, worldwide. That's good enough for me. LOA from Flight Design was issued for the install.
The antenna is a wire-whip type and pretty long. It is mounted on the bottom aft fuselage, same place where the old one was. It does stick down quite a bit, but not so low that it scrapes the ground, during landings, even in a high pitch attitude. However, when I am ground handling the airplane and lower the tail to an extreme, the antenna WILL make contact with the ground. Such an extreme lowering is not necessary, as it also threatens contact with the lower aft tail fairing.
The end of the antenna has a rubber tip on it. After landings, with a high touchdown pitch attitude, I have inspected the rubber trip for scrapes and found non so far.