The radial extent of a magnetised boundary plasma, or Scrape-Off-Layer (SOL), is determined by competition between transport processes parallel (||) and perpendicular (^) to the magnetic field B [1]. Whereas most aspects of || transport are well understood, ^ transport is generally anomalous, determined largely by turbulent processes [1], a situation common to many areas of plasma physics, eg. planetary magnetospheres, solar corona, wind, prominences and flares, magnetic accretion jets and many industrial plasmas. In nuclear fusion devices, the radial extent of the SOL determines the peak heat flux on the divertor tiles which poses a key constraint on the design and successful operation of a next-step tokamak, such as ITER [2]. In order to improve our predictive capability, physical understanding of the underlying ^ transport mechanisms is essential, especially in the reference regime of ITER, the so called ELMy H-mode [3]. With this aim, a series of experiments were carried out on JET in which power deposition widths lq were measured in several D and He plasmas, including scans in toroidal Bf and poloidal Bq fields, neutral beam power PNB and line average density <ne>. The aim of this letter is the interpretation of the above experiments, specifically the comparison of experimental lq with predictions of ~ thirty candidate models of ^ energy transport.