When you 'switch' to a .imgPTN file, the E2B partition disappears. So the \_ISO folder and all other files are no longer present.
The only reason to use imgPTN files for Windows Installs is to UEFI-boot. So if you need to choose from a range of different keys, you need to have a range of different XML files present.
You should make the .imgPTN file using Chandra's Split_WinISO utility and choose the MySetup.cmd option when offered.
I am afraid it involves editing a \auto.cmd file and knowledge of .cmd script language, etc. and is not for beginners.