Having shown that the peninsula Vestfjarðakjálkinn is more and less identical to Tröllaskagi and Austfirðir combined, we can have a look at the preconditions for the resemblance. There are two main volcanic zones in southern Iceland which can produce two similar areas at the same time.
The Western Volcanic Zone of South Iceland is the origin of Vestfirðir, while within the Eastern Volcanic Zone of South Iceland the Tröllaskagi and East Fjords regions split apart and drifted to different directions. Note that Borgarfjörður is marked with blue and the drifting path with blue arrows as according to tracing the vectors it is originated where the Westman Islands are located today.
This can be derived by following the vectors of tectonic drift of the map shown here, resulting from the two measurements of ISN93 and ISN2004. The results were published by the National Land Survey of Iceland in 2007 (Landmælingar Íslands – Mælingasvið in 2007, report No. LM-2007-01).
The fact that all of this drift follows the vectors of tectonic drift as measured directly as carefully as possible with stations of reference in Europe and America. The symmetry of Hornstrandir and Austfirðir of 22° compared with NS-axis is also a manifestation. The angle of rotation can also be calculated as the difference of alignment of convection rolls.
The resemblance of coastlines is so accurate that further investigation is needed to understand why the similarities of the areas are so accurate.