matsta31, you're correct, Tcase should be 4c higher than ambient. The 900 is a great case, however, if you followed the Test Setup to the letter, then it doesn't matter which case you're running, since the Test Setup is designed to level the playing field.
Regarding my writing style, thank you for your kind words. Good guess. Perhaps you might like to take a look at Page 3 of the Temp Guide's thread, 5th and 4th Posts from the bottom. You'll find the explanation there.