Re: Pick a better target.
Just some coffee-time, random, fly-by comments …
S. Teebas is correct.
We check the opponents hands/arms, but control is mainly focused on the entire opponent. The arms happen to be the connection point or “bridge” in this case.
“Pushing” or hitting doesn’t occur in the plain-vanilla style rolling exercise because the partners have agreed to stay with the plain-vanilla rolling rather than to capitalize on each others’ defects. Even so, part of the learning is to perceive those defects, however large or small. We learn and practice to “listen.” Intent even if not played out, is also practiced.
The degree of “sticking” that occurs is a function of the partner doing likewise. If the partner does not have proper position or intent, then there is some vulnerability on their part which, outside the confines of the exercise, you would capitalize on rather than to stick or chase their hands.
Similarly, the degree of sticking in chi sau would not occur in a normal “fight” unless both are Wing Chun (or similar). Of course, if they were both Wing Chun, why would they be fighting anyway? 
The rolling exercise is wasted effort and building of bad habits (for Wing Chun) without elbows and bodies correct. The deeper meaning of “sticking” requires proper positioning and intent, however “soft” or “hard” the mutual pressure may be.
When arm is in contact with opponent - said bridge being oiled, sweaty, or dry - I consider such things as …
- Is my position and intent such that [I]if[/I] the opponent applied more pressure, my elbows would be optimally positioned for self-protection? If not, then correct the body (everything) and elbows. [Of course there is some limit to how much pressure I can take even if well positioned, and eventually the partner/opponent might express enough that I would be required to turn. That is obviously outside the constraints of the standard poon sau/rolling exercise though.]
- Does the partner have elbows sufficiently positioned and with proper intent such that I would have to "force" my way in? Or do I perceive a free enough path that I [I]could[/I] slide up their arm and past their elbow to go in? Make mental note for future use. ;) [Once extending the chi sau to actually capitalize on errors, oil or sweat can assist this part, LOL.]
- Is the partner too "stiff" such that I could capitalize to uproot or off-balance them?
- Am I too stiff, rigid or telling such that the partner can utilize the bridge to upset me?
- Can I sense where the partner's center is? Can I keep my intent trained there throughout the endless dynamics of the rolling hands exercise and ever-changing hand/arm positions?
- Can the partner perceive my center? Can I be "relaxed" enough within my range of proper positions to hide that from him/her?
I’m not aiming to be comprehensive, but just to give exploratory examples. There are infinitely more questions along these lines, as well as issues that will vary with different partners (tall, short, narrow, wide, strong, weak, fast, slow, etc.). How can I perceive all these things and more through such a small and ever-changing contact area as the arms? [Aside for Andrew - I prefer arms to wrists, and practice quite “close.”]
It is definitely not about chasing hands. It is about minimizing one’s vulnerabilities and telegraphing as little information as possible while perceiving the partner’s/opponent’s vulnerabilities. And, eventually, how to leverage and capitalize on them. The bridge just happens to be the cooperative framework through which we do and feel these things in the rolling hands exercise.
Poon sau or luk sau is a very simple yet complex exercise. It’s largely about communication, and learning to “listen” and “read” (both oneself and the partner/opponent). The arms are transmitters. Wild, fast, strenuous rolling precludes the most profound discoveries. Chasing hands defeats the purpose. It’s about the whole person, not about the hands.
Again, just some random, non-comprehensive food for thought. Coffee finished. Have a great day.
Regards,