I have a question on expanding a pool. If I expand a pool from the same
storage that the pool is currently on, does that increase the risk of
failure? Im pretty sure it does not and only increases the risk when its
spanned across different hardware. Am I correct?

If it helps, the storage is DAS, running a RAID 5+ array and I have some
unallocated space left on that array that I would be increasing the volume