Naturally steaks will be thinner than 4 inches like thermometer needle, at least the one I have. So it will absorb less heat in total, and maybe show lesser values than what is actually inside the meat.
Problem two, meat is less cooked in the middle so how is that adjusted with thermometers? Will it still accurately show that it is medium rare for example?
When taking the temperature of a thinner steak, I pick the steak up with a set of tongs and insert the thermometer into its side. Aim to position the tip of the probe in the coolest part of the steak - probably the center and away from the bone, if it has one.
Your goal is to find the coolest temperature inside the steak.
The easiest answer, honestly, is to get a thermometer that doesn't have to be fully inserted. Some do require that, but many only need the very tip in, so you don't have to worry about anything besides making sure that the tip is in the center of the meat.
If that's not an option, though, Matt's answer is the best you can do.
