To participate in the contest it is essential to understand the logic behind, where can we get the information on how the contributor URS is calculated in detailed explanation and final URS determination

There is no Logic but take a look on the project whitepapers and the complete contest instructions. Contributor URS is calculated for example if your post obtained 52 as a verdict then reputation score 5.2 points are allocated to the contributor for that post.
Imagine if the contributor made 5 posts then he obtains,
For First post it is 15 Verdict, which is 1.5 points,
For Second post it is 35 Verdict, which is 3.5 points,
For Third post it is 50 Verdict, which is 5.0 Points,
For Fourth posts it is 72 Verdict, which is 7.2 Points and
For fifth post it is 100 verdict, which is 10 points.
To summarize this, final URS of the contributor will be 27.2 and the main challenging requirement is the quality parameter to achieve it.
Do take a look about Voter URS and criteria.