At least until a few days ago the numbers of Brent remained relatively low in Strangford with none at Lough Foyle - all suggestive that the vast majority of birds remain in western Iceland. Our friends there suggest small groups are widespread there in the usual haunts but we have no reports as yet from the 'big' sites in Faxafloi and Breidafjordur.
Within each of these large bays, whilst a range of smaller sites are used, the main concentrations are those at Akraos/Straumfjordur (Faxafloi) - the complex west of Borgarnes, and Alftafjordur (just east of Stykkisholmur) in Breidafjordur. The common denominator being that both sites have very large intertidal Zostera beds. Why rush past these when there's so much food available.
In previous autumn's we've seen these flocks of Brent getting disturbed or attacked by White-tailed Eagles and Gyrfalcon. Which in part explains when they come down to Ireland they take no chances when a Grey Heron flies past.