Smooth, controlled rolling harriers are soooo tough to master you really need a simulator. To get them smooth you really have to blend the inputs together. In a perfect world with NO WIND you'd have up elevator only when upright etc. if you wanted to go straight, but it really doesn't work out that way once you throw some wind into the mix.

Just practice a ton on the simulator and your thumbs will eventually figure it out but your brain never will grasp it fully