some thing i should have done before sending last post.
clicking arrow beside 'openpgp', shows 'sign message' checked. clicking arrow beside 's/mime', shows 'do not encrypt this message' checked.
if you change these setting and shorten your key, you will should still conform to pki and have a shorter sig.
also, in thunderbird window, click 'openpgp', click 'about openpgp' and go from there.