Sorry if this is a no brainer, I just want to make sure. Let's say I am using GF Dr Strange, a piece that has 18 defend , and piece that has 16impervious. Does the piece with imperv benefit from both making their defense 20 against range?

I'm no judge, but so long as adjacency is met, I say yes.

yes, back in the day I ran a lot of CT Invisible Girl with 18 defend With 3 ES/D figs with range. and I would park them in hindering for a 21D.

Thanks so much!

Yes.
First Replace, then Modify.
Defend is a replacement. Energy shield is a modifier

Awesome combo! I still have CT Invisible Girl, and she gets pulled out just for this kind of thing!

I used this Dr Strange with the 124 point Hulk from GG.

We had 200 point tourny and it felt like a very good combo, it did very well. Went 3-1 (I miscounted the range from some Star Trek Ships).