From what I have seen dell-recovery_1.60_all.deb is updating chroot.sh. This file is copied locally on the hard disk.
But I don't see this file on the Dell Recovery Media USB key. Same thing for the .deb package, I confirm it is not in the USB key generated.
I wil be in position to post the var/log/installer files in the coming days.
Another strange thing when you create directly the Dell Recovery Media USB key after Ubuntu/Dell configuration, an ISO file is created in the Download folder. But the ISO file is not bootable: it contains only one partition and not the EFI one.