Are they strict with backpack sizes? I do have a laptop bag (with a 13" macbook inside). The "handle" at the top of the backpack is quite firm, so makes the whole thing look bigger. In reality these days do they make people squish it in? I've paid for a checked bag (and I'm checking one); I just assumed a backpack would be fine... It definitely fits under a seat... For reference, flying DUB-MXP and PFO-DUB, if departure airport makes that much of a difference? YMMV situation?