[Werner]

Hallo Dann,
the plugs image is not perfect but not bad. The rear two plugs are also less sooty at my engine than the two from the front. They work there with hotter conditions.
In order to judge the plugs images correctly, you should travel 20 miles quickly, turn off the engine without running idle. Then you can rate the plugs face correctly.

Modern spark plugs are heat tolerant, because they have a "spread" (= multi-range) heat value.