Total number of docs on a shard in solr

Question

I am facing some issues when trying to understand how solr is generating score for a document on a shard. When I query the shard using q=*:* params the numFound param returns 25151. Next I give a query and try to understand the score generated for a document in the response. There I can see this log 2.3521233 = idf, computed as log((docCount+1)/(docFreq+1)) + 1 from:\n 278 = docFreq, number of documents containing term\n 25943 = docCount, total number of documents with field. The url I am using to query a particular shard is

http://mySolrUrl/solr/myColleciton_shard24_replica_t46/select?q=*:*&distrib=false&wt=json

So I have 2 questions.

1. As per my understanding the docCount should be equal to the numFound param which is 25151 but it is not?

2. log((25943+1)/(278+1)) + 1 is not equal to the calculated score. why is this? Any help here is appreciated. Thanks!