Q: But I thought moving a chord either a half step up or a half step down to the 'target chord' was a trick that works no matter what chord your playing?
A: in this school of thinking, 7th chords descending chromatically is a legit and normal thing, just like 7th chords moving down a fifth / up a fourth is considered legit. in either case, the internal tritone harmony (B and F notes in a G7 chord) can be seen as moving down chromatically regardless.