There are 2 different things:
1. What files will be scanned
2. How the files will be scanned, specifically - if they will be considered archive files and will be "tried" to decompress (and additionally scan the decompressed files)
If the ZIP extension is added to the "additional extensions" box, the files with .zip extension will be scanned. But if the "archive scanning" is not turned on for the Standard Shield, the files will not be scanned as ZIP archives (they will not be unpacked) - only the "outer" binary file will be scanned... so, eicar file packed inside will not be detected. If you rename eicar.com to ZIP, it will be detected. But if you compress eicar.com into a ZIP file, it will not (if the archive scanning is not selected).
If you start the Enhanced User Interface, you can edit the resident protection task and on the Packers page, select the ZIP (or any other) archive. Then, the content of the ZIP file (for example, the packed eicar) will be scanned by the Standard Shield provider.
Sometimes, the files will be detected even when they are packed to ZIP and the archive scanning is not selected - because they are "stored" - it means that the file has a ZIP header, but the actual data are not compressed. It is a special form of ZIP file - and it's the case for a number of recent worms. However, the detecion of eicar is different (eicar must be at the very beginning of the file to be detected - that's how it should be) - so, eicar will not be detected even in this case.