Tools > Options > Editing > General -> Line Insert Style
Can be set to before or after.
I'd like a 3rd option:
If the cursor is on column 1, then insert before, otherwise insert after.
This happens a lot, where I've got a line of text on the clipboard but I want to append it to the current line.
Whenever I paste, I get a line above instead of below - making it much harder to correctly join the lines.