Probably at no setting at all. Almost all scopes have fantasy range markings on the adjustable objective (AO). To rangefind put it on the highest mag and twiddle until in focus - do so at known ranges first and then put a bit of tape on the scope and mark the ranges on yourself. Everyones eyes are different but most scope makers must have weird eyes. Theres a nice article here about setting up a high mag scope.
http://www.airgunshed.co.uk/nefta/resources_head.htm