Moving dock between vertically arranged displays in OS X Mavericks and later
I have had success with my vertical arrangement by hovering the mouse in the orange areas to bring the dock to the top screen. On the bottom screen you can hover anywhere on the bottom of the monitor. 



In your case, where your monitors are almost the same size, it might be a bit tricky to find a spot on the bottom of the top monitor where the cursor wont slip through to the bottom screen and prevent the trigger.