Verify that the track is good and the surface sticks to the screen. Adjust the surface so that it just covers the screen. Draw a spline around a couple of the monitors that are on the same plane. Please do not use the 'Drag and drop here.' area at the bottom of the reply form. If you can give a little better workflow and design description, and post a screenshot on the forum using the toolbar it will help up help us help you. I'm not exactly sure what you are trying to do.

Mocha AE will only track the layer it is on, but you can apply Mocha to any layer, even if it is a nested comp. You can create masks from any Mocha Layer and copy them and paste them to other paths or create motion paths from them, or you can link to them with expressions. You can export the tracking data in 3 different formats from Mocha AE to any other layer. Each layer can track any surface inside the spline. Each layer can have as many splines as you need. Mocha can have as many layers as you like.

You can also get to those tutorials right from the Mocha/Help/Tutorials menu. If you are going to spend any time at all with Mocha AE you need to visit the Boris FX Tutorials Mocha Tutorials page and learn about the tool.

Mocha shape after effects