The Maze
So, you (mr./ms. whoever) get off from the Javelin at, say, pfm.13 and take the escalator to the ground floor in order to get a re-connection. You land at "the Circle", a non-orientational dead end by the Pancras road side, where (hopefully) signage tells you where to go next. Obviously first 180 degrees around, from the dead end.
a) Signage leads you to your EMT connection; around corner to the escalators and up to the platform turnstiles. That was easy, because:
b) your optional FCC connection leaves from pfm. B (B??

); to the right after ticket office, through turnstiles, down to mezzanine, down again after crossing the tracks. Phew. Arrival, in fact, isn't any simpler or faster, up double escalators again from pfm. A.
I still think a somewhat far cry from at-one-glance electronic "big boards" with train info and a single-level row of platforms in a single hall, all reachable from the same side and with HUGE number-signs in alphanumeric order above each bufferline. Couldn't get much simpler. (If you know that you'd be getting a particular TOC's service and know beforehand where the "sub-terminal" for that TOC is located, it's of course an improvement over last minute running to the other side of the shed, say KGX's pfm. zero; but for a first-timer - like at "STP
International?" - visible and non-confusing signage is paramount in these circumstances.)
And the map also shows that the (especially) non-international services have been moved exactly the length of the "old shed" away from, for example, the LU stations - all the domestic service platforms end under the flat-topped extension.