At work, I found myself maximizing Emacs horizontally and putting it at the bottom of the screen, so I decided to set this up to automate itself after Emacs starts. According to the Display Settings, I set the following elisp in a 1280 x 1024 resolution with normal icons on the taskbar:
(set-frame-width (selected-frame) 154)
(set-frame-position (selected-frame) 8 388)
It’s like you need to give a little distance from the left, so the frame border isn’t off the screen. The same is true to get it plumb with the very top of the screen. Here is a shrunk screen capture (click to double its size):
PS—Some of this didn’t work, so I used CLI arguments instead.