Hi,
BP components are the once that are responsible of running on ERP on the portal.
So for EHP6 sp 04 in the backend you can run on NW7.02 sp11 or NW 7.03 SP04 on the portal.
EHP is additional functionality and if you don't have both the version same the enhancement will not work but still existing functionality will work as of what sap says.
Thanks
Rishi abrol