I just wanted to add something. Before your post I was attempting to sysprep and capture with a different unattend file. Please see my information below.
I have 2 different unattend scripts that are mostly similar. For UEFI images (gpt partition, it creates 4 partitions (4 being set to extend) and the legacy creates 2 partitions.
I have issue with it capturing the entire drive with the UEFI script. I tested with the MBR script (Legacy) and it captured it fine again and only 11.2GB.