No. You can however create a new, second, SHR pool/volume with smaller drives. Read the Knowledge Center write-up. When expanding SHR volumes, added drives must be equal to or larger than the largest existing drive.
Otherwise, begin with the 4 TB drives, then add the 8s, and finally the 16s.
So even adding new empty drives, new drives must be same/bigger size.
So if I want to achive one big volume, I need add 4x4TB drives, then 2x8TB drives, then copy data from 16TB drives and…finaly erase 2x16TB drives and add them as last ones…