dora,

The idea is to soak the entire root zone which grows bigger over time. The movement of water through the soil (plume shape) is what you are interested in and depends on soil type. Sandy soil has a more vertical shaped plume than a clayey soil which is more horizontal. The placement will be what give you the best and quickest plume to cover your roots at mature growth. It is a trial and error process by running your system and finding out how far water travels in your soil in a certain time. You do this by probing a distance from your plant after watering to find the edge of the plume. I believe you will find out that two lines on either side of your plant about 6-12" away will work fine with infrequent and deep soakings( depends on the type of plant root size). Let us know what you end up trying. Aloha