Hi Thorben , 
Your request can only make us think back to Christian who had spent some time studying Hydropisphaera. No doubt he would have had an opinion on your quest. He left us exactly one year ago, you give us the opportunity to think of him.
I don't know if there are any mycologists today who study these Bionectriaceae. But there is no doubt that this collection deserves to be studied more closely. Knowing its anamorph would be useful (and molecular data, in a second time). In the meantime you can make a complete description, and in particular clarify some important points in this genus: are the ascomata completely glabrous, smooth ? or do they have hairs ? I advise you to show spore's ornamentation in the lactic cotton blue. A vertical section through lateral ascomata wall is helpful... (tha attached paper is a good model)
It's not excluded that this Hydropisphaera could be unpublished. The closest species is perhaps H. rufofusca, a species known from Indonesia. I don't know this one ,of course, and yours seems to be different.
Best wishes,

Alain

Another comparison suggested : H. boothii. Seems to be different, too (cf setae).

Hi Alain,

Every time I see some Nectriaceae-like mushrooms, I have to think of Christian.
He is undoubtedly missed, not only because of his expertise, but also as a helpful and friendly person.
Unfortunately, I was not allowed to meet him personally.

I have check the ascomata again and can't find any hairs.
In lactic cotton blue it's difficult to see any ornamentation, but there are some warts or spines.
You can see it good at the end of the spores.
But no matter what I do, I can't reproduce an ornament on the surface.
I hope my new pictures can help.

best regards,
Thorben