Hi Hilary and thanks for the reply.
SharePoint Designer (SPD) was always a 2nd best approach to my mind, and SPD is to be allowed in the future as simple workflows are sometimes needed to supplement the capabilities of the InfoPath forms, and although Flow will do the job, sometimes a SPD workflow is easier.
Using IE has the added advantage of ensuring that the permissions seem to be inherited correctly (assuming a user has switched to the appropriate Account login first of all in InfoPath 2013), and you get significantly less problems with Publishing if you've downloaded from a Library in the first instance.
However I just thought I'd check the approach again using SPD now (as I've not used it recently) and I've forgotten how to get the 'All Files' option displaying from within a Site. Under the Site Objects the last element visible to me is 'Site Groups' followed by 'Subsites' - 'All Files' as an option isn't listed or displayed. I do remember in the past seeing this though - what have I forgotten please?
Sorry to be such a numpty!
Alan C.