I have Decolux under cabinet lights. I don't know if there is a standard but our lights are right at the front of our 12" cabinets. Our backsplash is all lit up as well as the counter.
I'm sure this has come up before, why don't you try a search?

A recent thread about xenon lights:

Here is a link that might be useful: My xenon undercabinet lights are too hot

Placement has to do with the countertop. The lights should be centered on the counter. if your counter is 24" and the uppers are 12" then the lights should be at the front edge.

I think this depends on what sort of lights you use.

With the linear bulb strips (such as the Seagull linear I have) you just have a naked bulb with a small reflecter under it. When mounted at the front, it sends out light in the full 90 degree angle from down to the back. So it lights most of the counter as well as the backsplash. The ceiling lights get the rest of the counter in front of the cabinets.

I'm not familiar with those particular lights, but I think it would also depend on the depth of the light and how far down the cabinet-front comes down. If the front panel might block some of the light, take that into account in placement.

Thanks for all your responses. We will let you know what we decide. In the meantime, we have sent an email to the manufacturer of the lights for help!