hi, ffigueiredo, thanks for the reply, but unfortunately i already tried that and it didn't work...
adjusting the fog doesn't help because the fog doesn't affect the sky cube (of course, otherwise there would be no sky).
that's why i need the horizon... the bottom of the horizon image is dark because then the fog would make blocks not so noticeable against it... and then, when the blocks are clipped, i would see the dark horizon, and wouldn't notice the clipping... the problem is that instead of seeing the horizon, i'm seeing the sky behind it...
combining both into one single sky cube is something i thought of, but then i wouldn't get the same effect...

is this a bug?
because i can't think of a situation where you would use a sky cylinder, if not for a horizon image... and if the clipping doesn't work with it, i can't use it for a horizon... right?