I designed an isolated switchmode supply using an off-the-shelf surface mount transformer which is wound on an E shaped core with pins down 2 opposing sides. It works OK, but you can reduce noise by adding a grounded shield - for my prototype I made this from copper tape, wrapping around the transformer and looping round the sides which have no pins. It struck me, on the next PCB iteration I could make this a bit easier to manufacture by making a pad of copper under it to act as the length of "copper tape" which goes round the underside of the transformer. (Production quantities will be very low, maybe a dozen a year, so getting a custom transformer made wouldn't be cost-effective. And by making part of the "tape" a "track", I can recover from problems where a subcontracter delivers an already-mounted transformer he forgot to customise.)
So, to the question. It is a multilayer PCB. My first thought was, put this shield "track" on the surface immediately under the transformer, and run the tracks from the transformer pins - which loop from one to another under the transformer - on the next layer down. But then I thought, is it better to put the looping tracks between pins on that top layer, and bury the shield under them? That way, the shield goes round the outside of all the "windings":
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