Coming from the Balkans - like Gec- we have learned quite a lot on the partisan fights in wwII. Part of it was of course propaganda but definetly in the case of (ex) yugoslavians and (ex) soviets their actions really caused major disruptions of the axis plans. So did - at a smaller scale if i may use the comparative - the greeks . Now , coming o the issue of why the germans "masters of the war" did not have SAS-like actions behind the lines , i have a personal point by saying that it was practically impossible to achieve such thing since they were an Occupying Force , trying to invade a Foreign teritory, speaking a Different language , and most of all - having no support from the local indigen population. Without a hide-out - there's no Partisan - check the forest / villages where known partisan troups been confirmed.
And may i also say , having partisans against SS or Wehrmacht INSIDE Germany sounds like ...hm ...having partisans against Stalin or the Soviets at that same time in USSR.
Hope there will never be the case for similar activities...