The reason it works fine with the onebox and not with inline links is that they are treated differently. In order to create a onebox, the system first goes through all redirects to fetch the “final” unshortened URL. And because the final URL is recognized by the affiliate plugin, it gets rewritten. Unfortunately, the inline links do not.
I’ll submit a PR to affiliate plugin later with the support for
a.co
amzn.eu
amzn.to
Any other short domains come to mind?
From my observations, a.co and amzn.to are both short for amazon.com, so IMHO it would be safe to use affiliate_amazon_com tracking code.
amzn.eu translates to amazon.de for me, but I’m not sure if it might redirect to, say, amazon.fr for you. To accommodate both, I’ll add a new plugin setting for affiliate_amazon_eu.
Update:
PR submitted: