Hi Vigor,
I think you are right. This plant is very similar to Paul's P. Siamang.
I'm convinced that in the wild are many still unnamed natural hybrids. I attach the map where I marked species what grow in Sichuan and North Yunnan. We can see that areas of individual species are overlapped, so by my opinion there must be many F1 or F2, ... hybrids.
Sometimes is appeared some "new" species in China. I'm convinced, that 99,99% of them are natural hybrids.
K.