Years ago I was told that a taper needed to be at least an 8:1 ratio to look good and 20:1 would look even better.
I just tucked that note away and never gave it much thought until I started playing with the taper maker extension tool in SketchUp.
After playing around with the idea a bit I can’t make much out of such a rule. I think the person must have been describing some special case. It doesn’t seem to make sense to me as a general rule. I don’t plan on spending any more time thinking about it.