Please be sure to check out Geoclaim Contest Rules for full details about this feature in general.
The ownership percentage (%) is the likelihood that you will be selected for any given Geomine in that Geoclaim area.
Every geomine rewards a variable amount of COIN based on several factors, so you may be selected for a big Geomine or you may be selected for a very small Geomine or anything in between.
As a result, you can't expect the percentage (%) ownership to calculate the expected earnings since for example, one Geomine could have generated half the COIN earned as Geoclaim rewards in an area.
When do I get my Geoclaim rewards?