If your sketch is of the shape you're building then the curve and angle at the tip isn't going to be enough to matter. And if you use the MAC indicated by the diagram you posted the slight bit of area of the raked tip will simply mean that if you put the pivot right on the 25% of the MAC shown by the diagram that the little bit of tip area will mean that it's more like 24 or 23.5% instead of spot on 25%. And that's fine too. It'll just provide a light self centering force.