How to keep short celli notes from sounding fake

[epwpower]

As the notes become lower, the cello at least sounds somewhat more realistic, but as notes become higher, the cello often sounds "twangy", especially in higher velocities.

[Manolito Mystiq]

But, that's what a real cello does, too, right?

[JijGaat]

Get round robin patches, you can for an extra big sound layer pathes. The main thing is just to prevent to make it sound like a rifle gun. That can be assured by having as many different samples of the same note as possible.
And what manolito is saying is right. Just for the record: what samples are you using, and what are you finding hard to make it sound real?