I actually quickly fixed the visibility range and some other LOD bugs just after release, but my fix is a bit messy with LOD values edited in so many parts. Anyway, I decided to share what I have due to some visibility distance bug reports. This fix is still a bit WIP because I haven't had the time to check it properly and some parts like right vator and stab require some 3D work to get proper LODs for them. Anyway, it works and looks OK in game for me, so maybe it is useful for others also. If you want to see these beautiful planes a bit farther away, just unpack the attached meshes and let them replace existing ones. The fixed nose profile in v1.1 is already included.
I actually hope to see updated version with this kind of fix already included and hopefully with better LODs for right vator and stab.
In the FM side I'm actually still using Günther's first version with one small fix: I changed Wing_Mid to 3.16 and Wing_Out to 4.41 in [Arm] section to fix odd roll instability in dives caused by longer outer wing arms than wingspan. I'm not sure whether the engine running at too low RPM with lower airspeeds is realistic, but at least that feature makes dogfighting funnily challenging in D.520 and also in MB.152. I've also had some funny fights with that sharp stall, but I read that the real plane also had such behaviour.
Then one thing that might be some bug is that controls are easily broken when shooting at D.520 with MGs. Most of my bomber interception missions end with broken controls and AI pilots usually bail out in a hurry after first hits due to broken controls.