I am guessing that from what Tom just recently said, the placement of defending forces in a region will have to meet a certain ratio relative to the strength of the attacking forces in order for the attacking forces to not be able to land. So if you bring, for example, a 30k CS force to invade that rural region you will probably succeed even if it has 1k CS of militia.
It would be a bit silly to simply say that if a region has ANY defending forces a landing cannot happen no matter what. Put down 10 man militia units everywhere and bingo, no sea invasions.
