Keep the relative position of the line where the cursor is on the screen.
Write this line to your vimrc:
let g:cursor_lines = 0.3
That means the line where the cursor is on the screen will always 30% from the bottom relative to the vim window 's height. It can also be set to 40%, 50%. (let g:cursor_lines = 0.4, let g:cursor_lines = 0.5)