Ok, now that I am done with what I was doing...
The flashing you are using looks like it has size tabs on the inside of the ring. This allows you to buy 1 flashing and use it for the 3 most common size pipe jacks we find: 1", 1.5" and a 2". It looks like you did not pull the tab for a 2" jack which was perfect.
The neoprene is designed to fit tightly against the pipe but you problem is the outside diameter of a copper pipe is less than that of a PVC pipe. Enough that if you did pull the tab, it wouldn't fit and nothing would work but to replace the jack.
Standard Oatey jack but an older model. This jack doesn't have the size tabs on it.
It's important to make sure that the neoprene is covered with exterior paint. The best exterior paint that I have my guys use is an elastomeric based paint. **** is thick and does wonders on neglected stucco walls, or important flashings like the top of the chimney chase cap/pan. If, however, you do not paint the neoprene collar on the flashing, the sun will eat it up in about 10 years or so. Might be different where you live where you kinda get the sun.
This is what it will look like when the sun is able to get to it. Yes, this 1 is painted but painters will paint over anything - dry rot included - which they did here.
In the image above, someone slid down a different but thicker collar over this Oatey jack. This, however, wont do **** for the rest of the neoprene collar like we saw, as the collar was toast down to the flashing so, you need an oversized 1.
This oversized collar was installed on the jack I showed 2 pictures up. This unpainted collar will fit over the entire preinstalled collar on the Oatey. Notice that the tabs were not pulled on this one, so it is fitting tightly against the pipe. These are what you will want should anything happen to your pipe jack flashings.
Awe... nice and neat. No leaky for you.
