Just the fact that they want to hold on to Londonderry (70%+ Catholic) and Omagh (also 70%+) illustrates just who much of a really (even for the UDA) REALLY bad Idea this was. The map doesn't have enough detail to be sure, but it looks line they actually used the River Foyle (which runs through the center of town) as the border.
Most of the city is actually on the far bank (if you're coming from the Northern Ireland side of the city). There's not much on the near bank - Drumahoe and New Buildings (if you want to count them as both being part of Stroke rather than separate villages as they really are) are both Prod so if you're going to redraw the borders it makes sense for them to stay in the UK. Oher than that, all you're leaving in the UK is Altnagelvin Hospital, the Waterside estate (majority Prod) and Ebrington Barracks (which the British are unlikely to want to lose as it's the only major barracks in the area and a Brigade HQ. From memory, once we closed Ebrington down in the 2000s the HQ moved to Ballykelly but the Army may not want all that hassle back then). That plan also keeps Strathfoyle (where the docks for Londonderry are) and the City of Derry airport (the old RAF airfield at Eglington) in the UK.