500 Alien quad frame aka Reptile - H or X

[Quadcopter102]

I have put together a 500 Alien ( off ebay) frame and have a question.
Tuning up a FC ( CC3D - KK2) allows option to choose X frame or H frame.
Not really thinking other than a quad frame is a quad frame so therefore its X!
I just measured the distance between centre of motor shafts.
Front pair are 14.5 inches apart. (363mm (ish))
Diagonal pairs are 20 inches apart. (500mm)

Does this make it an H frame!
I seem to recall a vid on YouTube where some tech bod was running a calculations on this point, but I don't think anybody has mentioned this before.

 

[ringolong]

It is in-between if it is the one I am thinking about, but I would lean more towards the H.

 

[Quadcopter102]

I will get into the KK2 and change over to H and check what happens.