No ice or snow or any contamination is acceptable on the upper surface of the wings and, IMO, neither on the top nor bottom of the tailplane.
ABZ one winter night. Civil Argosy skip decided he didn't have to remove accumulations of snow and ice. Taxied out and found they couldn't get full UP elevator due snow/ice lying on curtain between elevator and tailplane.
Recollect, in some European country or other, I insisted upon steps being brought so that I could personally have a feel of the upper wing surface for ice. Ground handling not pleased. I fear that they failed to appreciate how great was the f--k I could not give about their feelings.
Ovda; ice on wings due sub zero fuel. Resident ESN employee chucked bucket of hot water over same. More ice to remove; longer delay.
B747. "You've left snow on top of wings" "It isn't much, you'll be OK!" (Red rag to bull effect). "We have pictures which will go to your CAA!" "We'll send the de-icer back."
In these situations only one person calls the shots. Why do people argue? They're only going to lose and possibly incur an ASR across their boss's desk.