11.9X average for 16X CAV is normal, that mode does not get a speed patch.
Don't think you tried the 12X write, which, unpatched, would be 12x CAV - start slow, continue rising to 12x at end, like the 16x. Being a plain 3/4 as fast as 16X all the way.
Patched, the 12X PCAV starts as fast as the 16X, rises to 12x and then levels off at 12X, so it loses less speed relative to 16X write, and may hold together better on media that suffers a bit of an error spike at the end if used at 16X.
If your media holds on well at 16X, then there's no real need to drop it to 12X.
Of course, the scanning ability of this drive is questionable, and needs the tweak to remove samsung from being scan disabled.