Well I took a look by myself and saw nothing wrong with it? I even drove 2 trucks next to each other, shot other with MG81z and other with handheld MG34, I aimed both at power lines that were above the target trucks and I got both trucks with same aiming point.
It might be possible, that tracers are dropping too fast, like they did on Vickers Mk VI (or do they still?). Hard to say as I tested this alone.