Bruce,
Thank you for the Question. In all honesty, it's a great question at hand. Depending on the player, There is a feel component to as what they should feel after impact while maintaining a flat wrist through impact. There are players such as Camillo Villegas who are very flat through impact and see a lot of controlled success in their flight and intended target line. It can also depend on the shot the person is trying to execute. Camillo is successful holding and or maintaining the wrist angle longer through impact, as he truly keeps the forarms connected and naturally allows the left forearm to turn over after impact. (Some may call him a trap player at times, which I'm not a big fan of unless the lie dpends on it or it's a specific shot at hand one is trying to create).
Then there are players I've worked with who try to maintain the wrist for too long a period through impact and clearly don't get the face / shaft as square and sycned creating weak blocks for the most part. Should you be the player who does this, focus on swinging slightly up post impact to keep the hands from leading too far forward after impact. At some point (unless you're truly trying to hit a fade starting left to your intended target line and ending up at your target line) one must have natural forearm rotation going into the finish. I'm a big fan of students using shoulder straps and hitting half controlled shots trying to slightly swing up through impact to identify the feeling of final release of wrists/forearms after impact. It's a natural sensation of forearm roll, not one that is forced by wrists.
Should you be a player who releases too early and doesn't maintain a flat left wrist (imagining you're a right handed player) I have them practice hitting into a smash bag without flipping it over feeling the sensation of a "flat" held left wrist post/at/through impact. Usually I will take clear cut video to see how successful they look at and after impact position (around a foot past impact). So you know, Many times one loses the angle they are trying to maintain through impact is a cause by starting from the top too quick and not allowing some level of lag to be created by pivot to leg transition. I'm sure you've had the sensation of over active hands from the top and not having the flush feeling you're looking for based on wrist angle. Many times it's in the back portion of the take away and transition that causes this. Half speed work on the range fixing those issues genrally gets the hands in a very good position at and through impact.
I appreciate your question Bruce. Hope this helps. Also Please email me at JFJPGA@GMAIL.COM to set up a lesson my friend. My hours are 4:00 to 9:00 weekdays and 10:00 to 4:00 Weekends. I look forward in working with you- Best - JJ