Easier said than done.

By having a curved seattube, it throws all the angles off.

Mounting the derailleur on the seat tube moves the derailleur forward, and in effect kicks the tail of the derailleur up.

It throws off the entire cage geometry, and you end up with capacity issues on the derailleur.

Perhaps also shifting issues as the derailleur is now directly over the midline of the chainrings, where the chain and teeth interface, rather than being behind the chainrings.

Thanks [MENTION=339610]Darth Lefty[/MENTION] for the research on the derailleur and manual.

Now, that is odd. The derailleur is apparently mounted to the rear swing arm/triangle. I think it makes some sense, as the derailleur typically overlays above the chainstays, and must be oriented with respect to the rear hub. So, with everything moving, you don't want the chainstays to bang into the derailleur, and angles would be somewhat better with the derailleur attached to the swing arm.

ScottDerailleur.jpg

I think the first thing is for the OP to get back to us on exactly how much vertical adjustment he has on the derailleur. One doesn't need a lot of clearance, but perhaps a little as everything on the rear moves, and isn't 100% centered with the bottom bracket.

It appears as if Scott uses a custom derailleur mounting bracket, so perhaps one could fabricate one's own bracket (which could be used to move the derailleur either upward or outward, or both.

To some extent, one can dimple chainstays for clearance, but I don't think I would do it on non-round aluminum.

Of course, there could be other derailleurs that might fit that direct mount that would have slightly different characteristics. Or, one could modify the cage slightly if needed.