Keep in mind the origin of this chart. I developed it for my own use so I could optimize my own burning with my media and my drives. Also, my standards are different from many other's. I expect my scans to be not only level and smooth, with peaks no higher than the low 20s, but I also want my total PIF and PIE to be as low as possible. My assumption is that totals will increase over time and I want the best chance for long term readability.
I have had great scans from my BenQ with TYG02 and I have had scans with hills and plateaus and PIF totals above 1000. While these are in no way bad burns, they are not what I see with my other drives and so I choose not to burn these on this drive.
BenQ 1620s are notorious for being very different, one drive from another, so I am certain that there are a lots of BenQ users who get better burns than I do. Also, because I scan almost everything, I probably pick up these variations where others don't. As well, I am certain my standards are higher than other's and are way beyond what is reasonable for peace of mind with most burns.
So don't worry. Burn away. Check your scans and see if they are OK for you.