Shkoder, I may not be able to answer your questions to your satisfaction, but I'll share what I know.
Historically, TTG02 seems to be good quality media (provided it's genuine TDK and not a fake with that mid code instead), although I have read where a few (2 or 3) had these same type of burns, albeit with different burners. What speed did your 716a burn this at? It would help to know this.
What I started doing was putting in a blank dvd and using 'media quality check' to see if autostrategy said the disk could be written at the maximum speed from the drop-down menu options. If it did not say 'media is judged as good,' I selected the next speed down and retested until I got the 'good' message; then I set my write speed to that and left A/S and P/R enabled.
Given Plextor's kind of 'hit and miss' approach with it's firmware and media support (i.e, some writing strategies not getting improved as they should have), it's possible this write strategy is one that wasn't improved. Generally when you have a steady increase in errors (Sum8/PIE), note the gb point where they start increasing and then pay attention to if your write speed increases at that point in your burning program (it APPEARS your write speed may increase at the 2gb on this graph, BUT that IS NOT certain by this graph alone). If it does, and the Px-716a isn't lowering the speed for you, then you'll need to see what the speed jumps to, and set the speed manually in your burn program so it doesn't make the next 'jump' to the speed that seems to increase the errors shown.
Try that. Perhaps some of the gurus like Dr.Pino, Zevia or someone else who burns every mid under the sun will tell you more, what problems they've had and how/if they solved them.