ZRTSI can't really set a shade to a specific position since the type of Somfy shades it controls don't send back information about their current position. It's a one-way interface. Personally, I'm using a generic z-wave dimmer device type and set the dimmer position to 50% to go to the custom position you would use the shade remote's Stop button (when it isn't moving.)
The ZRTSI can accept "Up" (On), "Down" (Off), and "Stop" commands though but I haven't found a driver that supports the Stop (to stop a shade that is currently moving up or down.)
