Huh, I would have thought a Lightheart Solong would be about perfect for you. I do have a cuben version of the normal length solo, or a cuben upper anyway (floor is silnylon).
I'm puzzled about the "quite a bit of water" comment anyway, though. Coming through the floor, or from above? Perhaps not seam sealed well along the top ridge, or ... ?

I have friends who have the standard (sil-nylon, not cuben) version of the Solo, and they like it fine, and have been in rain with it. My sense is that folks are pretty happy with the Lightheart tents in general, so ... you might ask your friend for details on just where the water was coming in. Any silnylon, or any other tent can get "quite a lot of water" given specific circumstances.

Put another way, if a Lightheart SoLong isn't going to be dry enough for you, I suspect then that no silnylon tent will, as the Lightheart tents are a sort of hybrid that's more double walled than single walled tent.