Here's how I do mat targeting:
(1) teach dog to target mat with all four feet. Click/Treat (hereafter c/t) for dog being on the mat. I don't care about position at this stage and the mat is usually pretty close to me.
(2) put mat farther away, send the dog to the mat, c/t for hitting it. Start with the mat being like 4 feet away, then move it to 10' or 20' or whatever you want. It is better to get a really strong behavior at 10' or 20' (when it's easy to reinforce the dog and do lots of repetitions to build up muscle memory) before you stretch too far on extending the distance.
(3) put mat even farther away, ask dog to target it, then ask the dog to do stuff while on the mat.
The reason I don't emphasize doing specific behaviors on the mat initially is because if you get a dog who thinks that the answer is to always run over and Sit on the mat, then you'll get a great distance Sit and have a much harder time getting anything else. So IMO it's better to mix it up and separate being on the mat from doing specific actions on the mat. Keep the mat itself as a pure target, then you can play around with it more easily.
If you want a Down on recall or other interrupted movement, put the dog in a Stay on one end of the training area, put the mat somewhere in the middle, recall the dog, and cue the Down when the dog crosses over the mat. The target operates as a secondary cue to get the behavior you want at a distance.
That's the part I'll make a video of when I get home, if you want, since for all the frivolous random things I tape my dogs doing, I apparently never recorded that specific bit.
(p.s. nice vid, Hunter!)