Well, I cant speak for the chroma pure patterns on the disk, only the calman patterns but I doubt they would be different. Its interesting that you see this with a Mitsubishi RP as that's what I use (wd-65837) and the differences I see are well within the meters claimed level of accuracy . I suppose the real question is how much of a difference are you seeing. is it enough of a difference that its going to be visible and/or is the difference so small that the sets controls would not be able to even adjust to compensate for the difference without throwing the result of even further?
Since your meter is a non contact meter that is susceptible to stray light contaminating the readings, I have to wonder if perhaps the reason you have different
readings with a field pattern could be the result of the meter reading the pattern across more of the screen. Since most screens don't have absolutely consistent light and color across the entire screen, having the pattern on the full screen could cause the meter to see these variations, causing a slightly different reading as a result. Ambient light can throw off a meter reading as well. With a field pattern there is more ambient light as a result of more light bouncing of walls. The color of the walls, ceilings and other reflective surfaces can pollute your meter readings.