The ECSC isn't as well defined as the ECC in terms of Working Areas and such like therefore it's arguable. The definition of Defined Cost in relation to people just says "... amount paid by the Contractor in Providing the Works .. for people employed by the Contractor".
So the answer is yes, provided you can demonstrate: (1) the amount has been paid, (2) it was paid in relation to Providing the Works i.e. the site agent, even though not on site was still working on the same job and not one for another client, and (3) the person is employed by the Contractor i.e. they have an employer / employee relationship with the Contractor (and not a contractor / subcontractor or contractor / consultant)
So the answer is yes, provided you can demonstrate: (1) the amount has been paid, (2) it was paid in relation to Providing the Works i.e. the site agent, even though not on site was still working on the same job and not one for another client, and (3) the person is employed by the Contractor i.e. they have an employer / employee relationship with the Contractor (and not a contractor / subcontractor or contractor / consultant)