Confused regarding @3x artwork for iPhone 6+ – Photoshop

I have an app in the App store to which I want to add @3x files. I read various posts but I am not sure how to proceed.

I read that coordinate space for the iPhone 6 plus is 414×736 points, (X3) that yields 1242×2208 pixels and not 1080×1920. Also I read that the iPhone 6+ will divide that by 1.15 before rendering to the display which will make it fit.

So lets say my App has a button image that is 44×44 pixels (the @2x file), then I should draw it as 44/2*3*1.15 to make it fit my 1242×2208 photoshop canvas. (/2 for points, times 3 for pixels *1.15 to overscale)

Now Apple documentation says @3x button need to have 66 pixels area, so that seems too small as it is not scaled up by 1.15.

This leads me to think my App canvas should be 1080×1920 which would avoid the iPhone having expensive rescale. So which is right? of course @3x would not be @3x.