perimeter drain / drain tile

CABO section 405.1 Why is it specified that the drain tile be covered by a minimum of 6 inches of stone as opposed to less? And what are the implications of there being less than 6 inches as I have encountered when I partially excavated a section of a foundation? Do I need to excavate the rest of the foundation and corect this deficiency to meet the code as written?

 

[ishvaaag]

I understand that the minimum height of permeable fill atop is to provide a minimum total section to allow the waters towards the channelization. It seems you are only losing the difference in height and in one side as net surface for water input(I assume this drain is aginst a wall, since the section of the channel itself should be capable enough to derive filtered waters). In any case, perfect compliance of the code means exactly that.

 

[ishvaaag]

Another possible consideration is the experience of less thick fills getting clogged, in which case the drainage capacity would result severely impaired.