Inadequate cooperation with Fritz! FON

At my Fritz! Box 7390 (in the basement) I ran a Gigaset sub-investment due to the low DECT range of the FB. Since the operation of sub-investment brings several drawbacks, I waited a long time longing for a solution in the form of an FB higher transmit power or a repeater.
After various experiments with repeaters third party failed (Tiptel, Siemens), because when changing from FB to the repeater occurred very annoying blaring or encrypted communication was ruled out with the hand parts, I put great hope in the AVM Repeater. This hope was disappointed: Range actually sufficiently extended. When changing from FB to the repeater (and back) there were no noise. But unfortunately some phones ringing sporadically with no longer. (They managed to achieve six phones, including Fritz! Fon MT-F, C3 and M2.)
The reason for the sporadic not ringing phones, I found out fairly quickly: The Fritz-Fons do not connect reliably with the device, which offers the strongest signal. So you can be registered with a single receive beams on the repeater and a walk to the FB right past without the phone logs on to the FB. In other areas of the house hand parts change every minute repeater between FB and back and forth, although the repeater has a much weaker signal. Since only a maximum of three devices on the repeaters can be logged at the same time play the phones at the repeater a kind of musical chairs. Depends is one of the phones in this game in the air, while a call comes in, it does not ring with; not even when it still while the other devices ring again with the FB connects.
Unfortunately works Murphies law so well that almost always the phone, which is a closest, not with ringing, triggering a mad scramble for a ringing phone.
I've experimented with various sites of the repeater without solving the problem.
Too bad. If yes can fold. I would hope that Fritz! Fons really only connect to the strongest signal the device and not switch back to a weaker signal back. That would solve my problem. Until then, there is unfortunately only one star because I'm going to again reactivate my Gigaset conditioning, which, incidentally, stands next to the FB in the basement and no problems illuminate the whole house.