Hi, your solution of cutting at the top of the arch is something I have thought of too but I was worried that it would reduce the curve. I think the initial problem is that mouldings (or the mould itself) were taken out too green and allowed to fully cure without support. Somehow that seems to have made its way into the moulds and hence the sag or droop. I have a genuine front 'clip' of the nose from a 246 but it's not on a chassis to take heights etc from.
Here is a comparison of a few Dinos to assess the differences - just remember that photos of this type do foreshorten and distort.
cheers
Ross
dinoreplicacomparison copy.jpg