In the above map, I've entered the positions of the Arthurian locations from the saints' lives, as well as Dinas Powis, a possible candidate for the fortress of Uther Pendragon (http://mistshadows.blogspot.com/2017/11/pa-gur-yv-y-porthaur-and-ruling-center.html).
Note that when Arthur appears at Aberystwyth in the VITA of St. Padarn, he is said to be "from foreign parts." Also, in the VITA of St. Illtud (cousin of Arthur), once the saint has visited the king's court he travels to King Pawl Penychen. Penychen was that part of Glamorgan between the Thaw and the Taff, wherein is situated Dinas Powis.
A discussion of my identification of Arthur's Dindraethou from the VITA of St. Carannog with the Cadbury hillfort north of Congresbury can be found in my book THE ARTHUR OF HISTORY.
The Dinas Powys and Dindraethou forts are literally directly across the Mouth of the Severn from each other.