So, if "cargo ships can charge more than seven times as much to bring a container from Asia to the U.S. as they can for the return trip", how long is waiting wo

So, if "cargo ships can charge more than seven times as much to bring a container from Asia to the U.S. as they can for the return trip", how long is waiting worth it? The answer should be one-seventh of the transit time, right? That is, if the detour to fill container with grain or rapeseed oil bottles adds more than 20% before it arrives back in China ready to be filled with factory goods, then it's a loss. That'll be only a few days. Quite a harsh time constraint. I feel sorry for those farmers.