horizon has a black band with HDRI sky

[El Rudo]

I'm quite new to Keyshot now trying to set up an open ocean scene with a bump textured ground plane as ocean and an HDRI image as sky. Somehow the sky doesn't seem to touch the ocean, there's a black band around it. I increased the ground plane size and resized and moved the HDRI down - yet to no avail. It looks like it's not the HDRI image but the water that becomes dark when it's further away from the camera.
Any tips?

[guest84672]

More than half of your HDRI is black. You may wan to adjust the hight and see wether you can make it disappear. Or use photograph of the sky as your backplate.

[El Rudo]

Thanks Thomas,
I zoomed out really far and found that the HDRI projection environment semi-sphere and the rectangular ground plane don't match. Moreover, when the ground plane is smaller than the semi-sphere, you can view though the gap and see the background color (black in my case). When the (corners of) the ground plane extend the sphere, some clipping of the sphere seems to occur.
I solved this by replacing the ground plane with a disc with the exact same Ø as the HRDI sphere (1000000mm for the sphere, scale X and Z of the disc by 10).