Per ProFootball Focus: https://www.profootballfocus.com/blog/2013/01/21/signature-stats-drop-rate-wide-receivers/
The stat is a percentage drop rate based, not on targets, but on "catchable" balls. Obviously, what is deemed catchable is somewhat subjective, but Avery and TY ranked # 1 & 2 (See second chart on page).
Hopefully TY will dedicate himself to working on that part of his game, but I think it makes a strong case for not bringing Avery back.
Imagine how much better Luck's season would have been if his # 2 & # 3 WR's didn't lead the NFL in dropped passes.