Believe it or not, there are several instances where Xiao Feng was made by Jin Yong to look extremely impotent. Here are the cases:
1) Unable to kill a tiger
2) Unable to kill Ah Zi with all his might
3) Unable to kill Ah Zhu instantly with all his might
Now, even people like Hao Datong should be able to accomplish these tasks, and yet Xiao Feng (who could accomplish much greater feats) could not. #2 and #3 can be considered plot devices, where the author needed Ah Zi to live and Ah Zhu to utter those final words. Specifically, I am interested in discussing case #3.
In DGSD, Xiao Feng launched a palm assault at Ah Zhu, the fake Duan Zhengchun. It hit fake Duan Zhengchun and knocked her back considerably. After this happened, Xiao Feng became puzzled as to why his opponent neither blocked nor withstood the attack.
Now consider a similar case. In HSDS, Zhang Wuji used all his might to launch a palm assault at Zhou Zhiruo. When their palms were about to meet, Zhang realized that Zhou did not use any strength to counter, so in that instant he retracted all his power.
Setting aside the million dollar question why Xiao Feng's palms, when making physical contact with the fake Duan Zhengchun's chest, did not feel the presence of her breasts... why didn't Xiao Feng retract his power? This is especially a taunting question since the principle of XL18Z is to be retractable at will (Hong Qigong said so). Alas, we must set aside the BILLION dollar fact that Jin Yong needed Ah Zhu to die in Xiao Feng's hands for the plot.
Some possible answers are:
1) Xiao Feng did not have the proficiency to retract his power once released.
2) Xiao Feng was not using XL18Z, so he couldn't apply XL18Z's retracting capabilities.
3) Xiao Feng was so determined to kill Duan Zhengchun that he prepared extra effort to make sure his palm power delivered maximum force under any circumstance.
The book did not seem to mention that he used XL18Z. Also in the third edition, Xiao Feng seemed to grasp all the principles of XL18Z's retracting and 30/70 rules.
So, what do you find to be the most logical explanation for Xiao Feng not retracting his palm at fake Duan Zhengchun? Plot device factor not withstanding.