What's the difference of three level configuation owner Global/Legal Entity/OU ?

Hi

   I do confused how ebTax is working on different configuration owner.

If we both defined tax rule on global configuration owner and OU or Legal Entity.  Then ebTax will first look into OU and LE configuration owner tax rule? if no tax rule condition meet, then it loop into Global Configuration Owner tax rule ??

Give a sample , I have two rule defined

Rule 1:

Rule Name: IC, Bill from <> Mexico , Bill To=Mexico

Rule Order:90

Configuration Owner: OU

Rule2

Rule: IMG, Ship from <> Mexico, Ship To=Mexico

Rule Order:40

Configuration Owner: Global Configuration Owner

If there is a invoice in Mexico OU, supplier ship from/Bill from US, ship to/bill to Mexico.