Or does shot stay level between 20 and 40 yards. I will be sighting in my shotgun tomorrow and want to figure on where to set my sights. Right now, I have 2 oz., 3 inch 6 shot in my Mossberg 9200 with a newly installed undertaker (copper and lead coated shot only) .665 and truglow sights.

I have killed two birds called into me by a buddy. One was at around 30 yards, the other about 40. The 40 yarder wasn't hit great, but didn't go anywhere either. Anyway, I was told if I put an extended choke tube in instead of my full choke, I can increase the range, or at least put more shot in the target at 40 than without it. But if I put the choke tube on, I'd need glow sights for increased accuracy because the shot would be so tight at 20 yards, I might now miss a bird at that distance I would have taken without the undertaker. So I went out and got the choke tube and sights, and want to sight it in. I'm wondering if it was worth all that trouble/money, especially considering how iffy it is to get a good combination of choke tube/shot!!!

If you know about patterns and shot guns, it is very hard to answer this question. Every gun shoots different. My Winchester won't shoot anything you have listed, choke or shell. And I dont care for Truglow sights. I just use the brass bead. I shoot 2 3/4", 1/4oz of copper #4 shot and kill turkeys at 40yds. As far as shot rising or falling that will change from shell to shell. Depends on the speed of the shot. But the pattern will open between 20 and 40 yds, no matter what choke you shoot. You will have to shoot the gun and figure it out.
Gselkhunter

There's not enough drop in 40 yd. to compensate for with sights. As far as whether the extra equipment being worth it, in all cases, you'll end up with a better pattern with an extended turkey tube than a factory flush full. They are expressly designed to be used with turkey loads.
Undertaker is a good tube. I use one myself. The board is full of reports of good results with them. With some patience and experimentation, I'm sure you'll find it was worth it. Have fun with it.