Assume one has borrowed a spool of wire, on the condition that one is
not allowed to cut it.

OK, say we'll make a folded dipole. Can one just ignore the unused
portion still on the reel beyond the contact clamp? We should roll it
away from the antenna a little, yes. Assume we have only used 1/2 the
wire. I suppose effects go up as frequency goes up. Probably the
best answer is to pick another design that will use the whole reel.

Bet Cebik never thought of this problem.