Problem with "hard coding" of prefix by grub-install

[Darryl Barlow]

I am running Manjaro on an encrypted btrfs partition.  UEFI system with GPT
partitioning.  Only other partition on the disk is a small efi partition.
The root partition was installed on the sub-volume @.  Boot is on the root
partition.  I moved @ to @Manjaro and made the necessary changes to the
configuration and to fstab.  Boot now fails and drops to a rescue prompt.
The grub prefix is still using @.  Apparently the prefix is derived from a
hardcoded value provided by grub-install.  update-grub and grub-install do
not fix the problem.  Nor did a complete re-install of grub from a chroot.
Advice appreciated.