Whels, that's because they flew high, many Mossies raids flew low and flew under radar.
Also, the B17's would usually have a duck and decoy, the decoy flying to another target to throw off the ground radar guys into thinking that the main formation was headed somewhere else.
JAB, yes, the previous threads on this subject mentioned the dot dar, which would detect ANY aircraft at ANY altitude,within a 25 mile radius...hmmm, now heres a thought, why not just include the GV's for this dot dar too? That solves the "under 500" issue, we can have both no bar dar under 500, and GV's will still be detected on dot dar...?