I got new Antennas from Circular-Wireless.com (the guy who made the 100km range record possible!
They look very promising. I went with SPW Antennas (receiver and sender) plus an additional helical directional antenna (the weird looking spiral). It should have the same 60degree horiz/vert "cone" of reception as my previous used 8dbi patch - but this new one has 11dbi gain!
This is what my other SPW / Cloverleave antennas look like:
Left: TX Cloverleaf - 3 "leafs" / Right: RX Skew Planar Wheel - 4 leafs
In comparison to normal rubber antennas they are much better. Nearly no dropouts while flying 360° around!
The only problem I had here: the soldering "knot" got loose due to vibrations - so signal was bad. After i fixed the soldering I covered everything with a 1cm diameter epoxy drop. This should be safe now! (not visible on the pic)