In Ming Dynasty General Qi Jiguang's Essential of the Fist manual, Stance #30 is the 當頭砲 (dang tou pao) "Block Head Cannon" stance. The 2nd verse reads as 虎直攛兩拳 (hu zhi cuan liang quan), which translates as "Throwing 2 fists straight forward like a tiger". Perhaps you may imagine yourself like a tiger pouncing forward at its prey with both paws extended.
In Chen Style Taiji, there is also a "Dang Tou Pao" technique by the exact same name. And you're literally supposed to throw 2 punches straight forward at the chest/abdomen region. Below is a video of people practicing this technique.
The first 2 persons appeared to have too much lordotic curve in their lumbar spine, which may contribute to poor power generation. Having a good spine posture is one of the most fundamental things in martial arts.
The 2nd thing that is tested is whether you're doing 含胸拔背 (han xiong ba bei) "Sink Chest, Expand Back" well. Your scapulae needs to be planted firmly on the back of your ribs for good structural stability when you extend your arms out forward. The final person in the video, at 45 secs onwards, seems to be doing quite well as his training partner got pushed back several steps.
I'm still working hard on the expanded version of Essential of the Fist. It's swelling to over 300 pages now, with lots of original drawings to explain my research. I look forward to releasing it soon!
Ancient Chinese Martial Arts Manuals