Personally, I think it's a bizarre distinction - I mean, I also believe HUMANS are more than the sum of their parts! So the Universe is too. Pantheism/Panentheism .. eh. Close enough to the same thing to me.
Others might argue, I'm really not picky on that one.
Speaking as someone who isn't a FlameKeeper (which is why I waited until you'd responded, Shad) but who
is a pantheist and definitely
not panentheist, I don't think they're the same thing, and I'd say that FlameKeeping's take on this is definitely more pantheistic. What distinguishes panentheism is that the Divine not only constitutes the Universe, but exists
beyond it. I don't think "greater than the sum of its parts" necessarily implies anything beyond/outside; just that
being the Universe, a cohesive and interacting whole, makes it greater than it would be if (
very hypothetically) the parts were separate (otherwise, one'd have to parse the description to "the Universe is greater than the Universe" - no, it's Universe All The Way Down

). The "negative spaces", the interactions and connections between the parts, are just as relevant as the parts themselves.
I may be projecting my own theories/beliefs here, but it seems to me that your stance is more, "There is no outside; it's all Universe."
Sunflower