Xara :: Transparent Object With Feather?

1) took a picture how a sunset looks at all above water

2) drew a rectangle and reproduced around the color transitions of the sun as an Elliptical fill

3) drew a rectangle for the water, applying fractal fill and transparency Stained glass to reflect the sun maybe, after feathered the edges

And here would be the question, it seems a horizont of the water is always rather a sharp line at sunsets, and in the meantime my water is feathered So how to make a trasparent feathered object on one side sharp, but in other way staying transparent feathered. My first thought was to Ctrl - K cloning of course and make it almost a line, but maybe there is one step method.