I've found out there is at least one time when a term "Lower Angren" is used in Baptism of Fire, in reference to the area where Ysgith is located. Could it mean that the Angren in the books is in fact Lower Angren, and there is another area called "Upper Angren" in Dol Angra, as on Komarek's and RED maps? That would be similar to Sodden case.
In the book Ysgith is situated north to the Yaruga (the hansa later plans to cross the river so that they can bypass it from the south). It's not the case in Thronebreaker (unless we assume Ysgith is on both shores but easier to bypass from the south). I'd assume the book one is Lower and the Upper begins further southeast.
Ok, so the context of the first fragment (Geralt lacking experience with Lower Angren) connected with the fact that they initially wanted to either continue their way in the northern part or to move south through Ysgith, I'd say that the southeastern part is Lower and northwestern Upper (makes sense also in a way that northern has many hils). But I might be missing some details, so I'll wait until tomorrow with changes.
It could also be that Angren is not divided by the Yaruga itself but maybe by another tributary or something, and that Upper and a small part of Lower (including half of Ysgith) are located North of the Yaruga, while major part of Lower and second half of Ysgith on the south (?)