Why is it that I can group like Rick Welch on a bag and Stevie Wonder on a 3D target(sorry Stevie) ???? Really.... I do.

Because you believe that you can't group on a 3D target.

If you can group on one type of target, you have everything that you need to group on any other target, except the belief that you can do it.

Check out Dr Kidd's chapter on "Why We Miss".  IMHO the best chapter in his excellent book.

I would reckon that it's because the bag will have spots & the 3D doesn't.

Because the bag target has a spot for you to aim at, you aim at that spot. A 3D doesn't have a distinct point for you to concentrate on & therefore you end up shooting at the entire target, not at a particular point. Take a magic marker & put a spot on your 3D, where you want to group your arrows & I would guarentee that your grouping will improve, instantly. Shooting instinctively requires a lot of focus & it does help to have something to focus on

Yes, robtattoo has it right.  Even with a compound and sights, shooting at animal targets is harder, because you are never quite sure where you are shooting!  That's why the gap shooters beat our brains out!  LOL!

One year my son shot everyday all year at flat targets and was getting tennis ball size groups consistently out to twenty yards. If he had one of six outside the group, he got way crabby and blamed any one or any thing on his extreme misfortune.  then when  deer season came he shot over the backs of two deer in a row, so he went out and got a deer target and shot the first dozen shots at it and inch over its back.  I told him to think of it as a rubber back stop, then he shot the heart out of the poor thing.
If I could only get myself to believe that, maybe I would do better at 3d events.

"Sheep are a peculiar crowd." -Big Bad Wolf.

I do try to concentrate on a spot on the 3D.I really believe that I'm peeking for the arrow.

I could not hit my foam as well. I put a tack on my foam critters and yes "thankfully" I have had to replace said tacks numerous times  

tack idea worked for me also, now when hunting just need my son to run put a tack in the biggest buck for me.
oz

Here's what happens to me. I shoot a good group if I can't see the "spot" or the arrows perfectly. I'm focused on a "center" of a zone, and the arrows click in together - tight. This first happened in poor light -focused on the "center".

When I shoot at a spot, I can hit it. But when I'm shooting at an arrow, or an existing group, I start missing. I'm unconsciously unwilling to bust an arrow. I call it "Robin Hoods Panic".

Dang arrows cost five bucks!