Hi Wantok,
I haven't looked at EV yet, but I do have it here. As far as I can see there is a link word between the part of the clue that is the definition and the part that is the 'cryptic' bit. It is the link word you insert. If you have any letters in any of the asterisked clues let me know on this thread (if no-one else gives you any help) and I'll work on those first.
You need to take an "average" (mean).
Solving 1d for example you arrive at TACTIC and ZIGZAG. Midway between T and Z is W, A and I is E etc. The MEAN word ends up as WEEWEE, which is entered into the grid!
Question: Is 17 down RUKH?
Normal Clue: Bird missing parties at Princeton?
Starts RU and could end with H