combining of the write operations can happen when the IOs are sequential. Those combined IOs will translate to FSW . Not sure about the other two "width" components you are referring.
Detailed information about Dynamic Pools can be found in the "DELL EMC UNITY: DYNAMIC POOLS - Overview" white paper. Disk Extents are similar to what was called Element Size on CLARiiON and VNX. Stripe Width on CLARiiON and VNX is the same as Raid Extents on Unity in Dynamic Pools.
From page 9
RAID extents are created with the remaining drive extents. A RAID extent is a collection of drive extents which complete the RAID width chosen for a particular RAID type. For example, if RAID 5 was selected as the RAID type, and 4+1 was selected as the RAID width for the Pool, the RAID extent would contain 5 drive extents (4+1). One for each element of the RAID width. The RAID extent provides RAID protection for user data stored within the Dynamic Pool, and is later used to provide usable capacity to the Pool for storage resource creation. A single RAID extent cannot contain two drive extents from a single drive for protection purposes. Also, RAID extents must contain drive extents from only a single drive partnership group.