No matter where you physically put the second monitor, you may still need to mouse scroll off laterally(left or right depending on how the 2nd display was detected) to get to the other monitor. That is the only jarring thing I could see happening. I don't know if landscaping the displays makes that different or not.
My 2nd display is off to the right side of my main display. I usually just alt+tab to a window that I previously moved to the second display, to access it. That is one way you could avoid side scrolling to the second display.