I have a collection with 300,000 documents. In collection there is a 2dsphere index on 'geo' field.

Here is a query I run:
db.runCommand(

{ geoNear: "around_test", near: [59.6048899000000030, 36.2774393999999990], num: 500, spherical:true, query: null, }

);

Stats of this query are weird:
stats:

{ "nscanned" : 103971, "objectsLoaded" : 80166, "avgDistance" : 0.1816846648955057, "maxDistance" : 0.1955302102158397, "time" : 1124 }

In the query I limit results to 500 documents. But in stats I see that mongoDB reads 80166 (objectsLoaded) documents from disk and only then cuts it out.
No need to read extra documents from disk if there is a limit on result length.