Xcode Image Asset By Device

Question

My question relates to creating a custom image asset for iPad Pro. It is my understanding that the correct image from an image asset set in Xcode is picked based on the type of device in the following way:

iPhone:
  1x: iPhones older than iPhone 4
  2x: iPhone 4/4s, 5/5s, 6/6s
  3x: iPhone 6/6s Plus

iPad:
  1x: non-retina iPads
  2x: retina iPads (including iPad mini)

If this understanding is incorrect, please let me know. But if it is correct, how do I make a custom image set for iPad Pro? The images I made for the regular-size retina iPad would be too small to fit on the iPad Pro and there is no 3x option for an iPad image set.