Again I totally accept the logic BUT where is it written down?
ATIS
27R 270/10 10km ovc011 9/5 1023
Would you have made an anti-ice perf correction? I wouldn't have for the last couple of decades. I would have thought this would have come out in at some stage in the past. Perhaps I've always missed it but no FO I've flown with has ever made an Anti-ice correction in the above corrections.