Ray,

Several schools of thought about tippet to fly knots. As far as I know, there are no 'accepted' norms.

Some feel that faster (or perhaps 'easier'), even though weaker, is best, and you get the clinch knot folks and the other 'quick' knots.

Some prefer stronger knots (there are lots of those out there, most are more difficult or take longer to tie).

In my albeit non scientific testing, adding an overhand knot to a clinch knot does not make it less likely to slip or cause it to be any stronger. Doing the improved clinch knot does add strength. Though it's still not a very strong knot, going the 'improved' route will give you more results than adding the overhand knot will.

Up to you, of course. What knot a fisherman uses is intensely personal.

Buddy