Restoring Windows Image Backup to same drives in different computer

I have a Dell Precision T5400 with two 500 GB hard drives in RAID 1 using the motherboard RAID controller. I ran out of expansion room in the case, so I am moving to a Precision T7500, also with built-in RAID. I have done this before, but never with RAID enabled.

On the cheap Dell RAID cards, it appears creating a RAID array always wipes the disks, even when they were part of the same type of RAID array on a different system. To get around that, I used Windows Backup and Restore to create a System Image on an external hard drive. The image includes a 500 MB system partition and a ~456 GB primary partition.

When I boot into recovery mode on the T7500 to restore the image, it gives me an error:

System image restore failed. Disk set as active in BIOS is too small to recover the original system disk. Replace the disk with a larger one and retry the operation (0x80042407)

This is despite the disks in the machine being exactly the same ones that were in the old machine. WinPE sees the RAID array just fine and there are no other disks in the machine which could be the active disk.

I tested the image and I can restore it to a 1TB drive (so I know the image is OK), but that drive is old and has known reliability issues, so I can't just use it (plus I still want RAID 1).

How can I get this image to restore?