That's what I thought at first too @
KLouis but unfortunately it doesn't work this way... Half a year and roughly 22-24 A3 flights into this great new A3 policy my experience so far is as follows (percentages are approximate):
- 65% of the times I ve been given an upfront seat, and in particular
--
50% a middle seat 
--
15% an aisle seat
--
0% a window seat (or perhaps 4%? maybe once, I am not sure)
- 30% percent of the times stowed in the high 20s
- 5% percent (just once) I ve been assigned an extra legroom seat
Things that don't seem to matter:
- Fare class/price: I ve been given upfront (and my only extra legroom) seats on promo U and P tickets. I ve been thrown in 24D on M or H tickets.
- Check-in time: It appears that your seat may be pre-assigned whatsoever (?)
Anyway, as an 1.9m tall barbarian I end up buying my upfront/extra legroom seat, especially for longer flights on the A321s. Pitch on the seats in the back is among the tightest I ve seen in a full-service carrier, my legs literally can't fit unless I turn my knees facing sideways
And I am not even unusually or extremely tall...
Advice in case you decide to buy a seat: Go for rows 1 to 5 or an emergency exit row. Although rows 6-10 are marketed (and priced) as "up-front" seats, they offer no extra legroom compared to the seats in the rear. (On a couple of planes -A321s I think- also row 6 offers some extra legroom.) Most likely in Greek destinations you won't get to get off quickly either since either there are no jetsteps (smaller airports) or they avoid using them. (Oh well, technically you will board the bus among the first and wait there for the rest of the pax, but that's not my idea of getting off the plane first
) So if this is what you are interested in (and not comfort) the last five rows work equally well.
What I moreover find annoying (but that's more personal) is this 2 euro charge for booking a seat in Greek domestic flights. Especially in flights booked by my employer, I have to retrieve the booking, select a seat, enter my full card details, and hope that their website is not "temporarily unable to process the payment" so that I need to "please try again later", and all this hassle for 2 euro on a 130 euro ticket...