This work started at the ‘Interdisciplinary Workshop on ‘Models, simulations and data at LHC’ in Edinburgh, and continued in the 2015 Les Houches meeting on TeV-scale physics and two MCnet schools in Göttingen. The authors thank the organisers, especially Michela Massimi, Fawzi Boudjema and Steffen Schumann. They also thank Josh McFayden for useful discussions, and STFC for financial support. This work was supported in part by the European Union as part of the FP7 Marie Curie Initial Training Network MCnetITN (PITN-GA-2012-315877). MK is supported by the German Research Foundation DFG through the research unit 2239 “New physics at the LHC”.