Camellia roots are shallow so I think you are watering too long if it comes out to 5gallons per dripper. How big are these shrubs? I have mine set to water 1g in one hour and they water twice a week, three times when the temps are in the 100s. 5 gallons via two drippers means you are watering the shrub 10gallons! I would water less and more often. To tell if there are areas that are dry, just insert a finger to a depth of 4" (not counting the mulch) in several places around the main trunk and see if it feels dry most or wet. Sasanquas get rid of old leaves this time of the year so it is hard to tell if the yellow leaves are caused by that or not.

Another suggestion in order to clarify. For about a week or more, check the soil moisture daily by inserting a finger to a depth of 4" somewhere inside the drip line of the bush; do not count the mulch when measuring the depth.

If the soil feels almost dry or dry then water 2-3g and write down on a calendar when you watered. Start from the root ball outwards past the drip line. Do this for a while until you notice a watering pattern developing in the calendar; in other words, observe if you have to water every 2, 3, 4 or 5 days. Then set your sprinkler or drip to water early in the mornings about 2-3g of water on that frequency.

If the temperatures change 10-15 degrees (up or down) and stay there, check using the finger method again and adjust as necessary. I now have to water about twice a week due to the high temperatures in the summer and may have to switch to three times when I get to the 100s as these temperatures are accompanied by drying winds which dry out the shallow camellia roots first. But by September I am back to watering as I usually do in the Spring.