Peter, it is very inspiring that you could see the tidal tail in a 16"! I should give it a go in my 18", but probably after I get new coatings. It's unfortunate that very few tidal tails are accessible in 16"~18" scopes.

Here is an observation of the object from the Leviathan of Fort Davis (Jimi's telescope) with a 7mm Takahashi eyepiece on the same night (TSP 2016) that Jimi described in the post:

NGC6621.jpg

a, d: very easy
g: The upper part of the tidal tail is the most evident and thick
b: Much fainter than appears in the image. Somewhat stellar. (Someone in the group told me it's probably a stellar association whose formation was triggered by collision.)
e: Spiral arm evident.
f: Easier knot
c: Harder knot
h: Knot in the tidal tail, hardest.

Ease: a ~ d > g > f > e > c > b > h. During moments of great seeing, one could see mottling of the tidal tail! Photographic!!!

We also took a look at this object in Bob Douglas' 28" at GSSP a few weeks ago -- the tidal tail was not difficult to see.

Clear Skies

Regards
Akarsh