How to get both window position and size correct in this RDP file?

I have two displays configured like this:

enter image description here

Primary display 1 is on the right, it’s 1920×1080. Second display (#2) is on the left, it’s 3840×2160. They are aligned at the bottom.

If I run mstsc.exe /l I get this output:

enter image description here

I am trying to write an RDP file that starts the remote session in a 2560×1440 window on display #2. The closest I can get to what I want is this:

screen mode id:i:1
use multimon:i:0
desktopwidth:i:2560
desktopheight:i:1440
session bpp:i:32
winposstr:s:0,1,-3200,-754,-607,685
smart sizing:i:0

Which results in a window with a vertical scrollbar:

enter image description here

Note the vertical scrollbar on the right of the window. The bottom portion of the remote session is not visible unless I scroll down or resize the window.

It seems perfectly logical that all I need to do is increase the last value of winposstr. But any value higher than 685 results in a change in the window position. For example, this:

screen mode id:i:1
use multimon:i:0
desktopwidth:i:2560
desktopheight:i:1440
session bpp:i:32
winposstr:s:0,1,-3200,-754,-607,686
smart sizing:i:0

Results in this:

enter image description here

Have I encountered a bug in mstsc.exe? Or am I doing something wrong with winposstr or some other setting? What I want is a window positioned like the first screenshot, but properly vertically sized so that there is no vertical scrollbar.