Hi,
Finding methods only apply to traffic sources (search engine, paid/natural) and expiration is visit, obviously.
You can set the expiration of eVars independent from findings, e.g. expiration after a purchase event.
Keep in mind, that your eVar with expiration "purchase" means, that a purchase is also counted to your eVar after the visit, eg. eVar is set today, but the user make the purchase ony week later ...
Cheers,
Michael