I cant see the picture here at work but you can either cut the brush I beleve which is a button on the editor or you can make the brush you want in the 2dcreator.
I checked is it tank visible when is behind the building. It's the same... and this is only 500m. So in RO really aren't any ways to do something that tank would be invisible? Beacuse if can't so what is sense of hiding behind bushes or buildings? This is a serious bug in RO, it looks like that you can't hide anywhere... except for hills. It can't do any ambush, anything... I hope that guys from TripWire do something with that and will be fixed in next update...
Send a PM to Divinehammer