How deep do you need to insert the probe in a piece of meat to guarantee accuracy? I have a wired thermometer that I mainly use for roasts, which can support the entire probe inside the meat.  However, I used it last night to cook some country style ribs (pork) and was only able to insert the probe about half-way into the rib.  It wasn't touching any bone and when I calibrated it, it still read true. Anyway, when the alarm went off on the pork (I set the alarm for 160 expecting the temp to coast up to 165), it was still massively underdone. The probe lacks the dimples that I am familar with on my instant read thermometers and I would like to know if anyone has run into a problem like this before.  All I can think is that the heat from the oven was being read off the back side of the probe.  The tool is so useful that I would hate to regulate it to roast only duty but I have no idea how to fix this so it will work accurately.
My theory is that the probe should be inserted into the part of the meat that will be the last to heat up. For a roast without bones, that will be pretty much be the center of mass.

For something with bone it, I would aim for a point somewhere between halfway and 2/3 the distance from the skin to the bone in the place where that distance is the largest.

Are you checking the temperature while the meat is still in the oven/on the grill? For a large meat where the entire probe is in, there will be no effect. But for a thin piece of meat with just the tip inside the meat, the air temp and radiated energy will throw off the results. Either insert it length-wise in between the ribs, or set the ribs on the counter to check the temp.

If you are still getting inaccurate results after this, then I would suspect the accuracy of the thermometer.