I must say I'm a bit surprised that the school's case is that they have physical constraints which would impede them going over PAN, yet from next year their PAN is being increased by 8 anyway. I can only hope they are just going through the motions & wouldn't actually mind a few extra.
The PAN isn't just worked out on that school, but by looking at all the schools in the area and the number of pupils who need places. A school can not admit over PAN, unless forced to do so by an appeals panel...
If I were you, I'd ask the school side about next year, as well as asking if current numbers cause a problem. You may get a knowing grin from either the panel, the LEA, or both. However, you asking the question will not guarantee that you win the appeal. There may well be other parents asking the same question, and even if they don't, I'm sure the panel will (well, I would if I was on that panel). It will still be down to how good your case is that your DS should have a place & is bright enough to cope.