We've had a bit of a raging debate on this issue. There was a thread somewhere where this was discussed.

Many of us were convinced the space on the 788/9 was bigger and I noticed it when I was on a few flights.

So I decided to do some mild measuring.

One of the major irritants is that the table cannot be stored so it is not in the way. And when the seat is in lie-flat position, I found side-sleeping impossible as the table would hit my legs.

Anyway, IIRC, I one posted that the only ones who know the exact dimensions are the manufacturer and AC and neither are going to share.

3 inches makes a huge difference. (Yes, you can all laugh now)