You're going to need to calibrate what 6" means in terms of pixels, and one way to do that is to make a grid or a full screen of letters for your projector then find the exact places that the bar cuts them off.
Next place your clip on the timeline then double-click on it to open the PiP Designer. Click on the Mask tab and select the one near the bottom with half the area covered. You'll also need to uncheck the
Maintain mask aspect ratio box and drag the left & right edges to fill the screen. It should look like this:
Click Save, then copy the clip and paste the new copy on the track directly below the original so they're in sync. Open the new clip in the PiP Designer, go to the Mask tab and check the
Invert mask box. You should now see the right half of your clip.
The next step is to move each side of the clip away from the center, so with the right half open click on the Properties tab and set the
Position X value to 0.550 to start with. Click Save and open the original clip and change its
Position X value to 0.450 the click Save.
You'll now have each half split down the center, and you'll then have to play around with the spacing to get the width between the clips just right. Increasing the
Position X control shifts the clip to the right; decreasing it moves to the left. Each count = 1 pixel. If you put a piece of tape on your screen that marks where your cutoff is from the first step, you can click the up/down arrow for the
Position X control and dial in the exact offset value.
The good news is that once you've got everything calibrated like this, you're free to change the content at any time by dragging a new clip directly onto the left or right section then choose Replace. The new clips will then have the correct spacing.