Addon Domain Access Question

My understanding on Addon domains was that the .htaccess file at the main domain would apply and filter to the Addon domains. For example:

mymaindomain.com (the main domain on my shared account)
-- my1staddon.com (Addon domain #1)
-- my2ndaddon.com (Addon domain #2)
-- my3rdaddon.com (Addon domain #3)

I very clearly have an entry in my main domain .htaccess file as follows:

deny from 93.158.

However, I still see hits on one of my Addon domains coming from 93.158.148.31.

I've gone ahead and added another .htaccess file at the Addon domain level to attempt to block that IP range, and will see if that works.

But was I wrong in thinking that the top level .htaccess file should also apply to all Addon domains?

Thanks!