Auto-format: wrapping later in line when inserting text

Question

After reading help textwith and help fo-table, I expected that when I set

set textwidth=20  " for demonstration
set formatoptions=tcq

then inserting text would always eventually cause a line to wrap, but that isn't the case. Wrapping only happens at (or before) my cursor. And if I paste, wrapping doesn't happen at all.

Example (Vim 7.4):

12345678901234567890
This is a long line

The line will auto-wrap if I hit A and start typing.

But if I hit 02wi and type "still ", it doesn't wrap:

12345678901234567890
This is still a long line

I have to type another 7 characters before it will wrap, and then the problem continues on the next line:

12345678901234567890
This is still more <-- it wraps here
typing and again a long line

Pasting doesn't trigger a wrap either:

12345678901234567890
This is a long line This text is pasted and not wrapped

I think what I want is set fo+=a but that applies at the paragraph level, whereas I don't want auto-formatting of one line to spread to other lines.

Or am I missing an option?

To be clear, after launching vim -u NONE, this is what I type (less comments):

:set textwidth=20<CR>
:set formatoptions=tcq<CR>
iThis is a long line<ESC>
02wistill <ESC>                " no wrap happens, but I'd like it to
u
:let @r = "This text is pasted and not wrapped"<CR>
$"rp                           " no wrap happens, but I'd like it to

Answer 1

I came across a partial solution, using formatoptions=tcqaw. Basically, you still auto-wrap paragraphs, but a paragraph ends when the line has no trailing whitespace, which is suitable for many cases.

Using your example (with a slight modification, no undo and using "<SPACE>This...") I get this result:

This is still a long  
This is pasted and 
not wrapped
line