Shouldn’t be at treetop level, IIRC medium and small try for 200 feet clearance, bigger ones somewhat higher.
And attack paths are crucial, that’s what the ‘bird dog’ guide aircraft are for.
Two tankers lost in BC several years ago because they did not follow guide aircraft’s instructions - judging varying terrain with trees on it is very difficult, fatal fools did not turn into valley as told to.
Martin Mars lost in BC early in history of that operation, perhaps flying uphill after drop which is not wise path, possibility that drop doors did not open to release load.
10Tanker drug gear and flaps through trees one day, a very close call.
Coulson lost a C130 in Australia a few years ago, investigation ongoing, was flying in gently rising terrain and circling after partial drop, hit a big tree.