You guys (other than Aguila Blanca) miss the part where the OP says he "open's up" to shooting 2 inches @ 7 yards?
He says that it "opens up to 2 inches", not that the shots stay within a nice tight group that cluster 2 inches away from where he's shooting.
I take that to mean the group size opens up to 2 inches. That has zero to do with the velocity difference and/or the weight difference between slugs.
This is all either the shooter shifting his eyes from the front sight to the target to see where his shots are impacting - - or - - not concentrating on the basics because of the lesser recoil of the .38 special.
I doubt it's the former, because he sounds like a pretty disciplined shooter when he says his shooting "opens up to 2". 99.9% of the people here would brag about shooting a 2" group at any distance, so, IMHO, we're dealing with someone that is a bit above the unwashed masses.
That leaves the latter - he's fudging the shots by getting a little loosey goosey. That's nothing more than a different flavor of flinch.
& one of the cures for flinch is - - play mix it up with the ammunition, just like I stated above.
Now- try it at 25 yards & see what you get.
Why on Earth would he even consider doing anything like that? That's a pretty ridiculous statement to make - even in jest. The whole object is to help the OP, not do something that would even further his frustration.
If he's having problems close in, then moving back - to insure he's going to not only fail, but, fail miserably, does nothing to help.