After submitting the answer I started to doubt it myself and read a few posts and comments about the hardfork. It seems that the I was wrong . Every root level comment seems to be a direct reply to the post. Every root level comment has a weight which determines your final post reward. This weight is slightly different based on commenters steem power. But when you make more than 4 posts in 24 hours - the weight is decreased from 100% to a smaller percentage. So lets say that the average root level comment weight is 2.05 (random example) and you get 10 root level comments then if you post more often than once in 6 hours, the total reward will be 2.05 * 10 * 0.8 (an example of 20% root level comment weight reduction) instead of 2.05 * 10 * 1
Also keep your eye on this thread - people have the same dilemma there:
https://steemit.com/steemit/@ervin-lemark/steem-0-12-0-hardfork-this-tuesday-will-bring-spamming-penalty-if-you-will-post-more-than-4-posts-in-24-hours
RE: July 26 Steem Hardfork Question - Issue #176 - Definition of Root Level Comment?