This is only the second biggest mystery with the 789 seat map. The center seats are a bit offset because the Prem+ cabin sits back a bit further in the middle (because of Polaris) so there's less room for the same number of rows. It may well be that they have more leg room than the other E- seats as a result, but it's not E+ amounts.

(The biggest mystery is why 34JKL are E- but 34ABC are E+. I have looked repeatedly and cannot find a noticeable difference between the two sides or offsets. Mind you, it's usually dark when I've looked . . . but still.)

You might want to have a look through this thread: Everything You Want to Know about Where to Sit on the 789 true Polaris and PP version - Page 7 - FlyerTalk Forums

(And mods may want to move this there eventually).