In a heavier organic soils you might get away with less carrots per container than a lighter coco based mix. Fabric pots drain faster than plastic does. Ambient temps and humidity are another factor.
There are a few different designs of bluemat "carrots:" the ones made for indoor plants can be set with multiple drip points and are smaller than those with only one drip point but the slightly larger carrots hold more water for outdoor plants. They even sell super long carrots for trees and shrubs, etc.
You'll need to fiddle with the valves to set the proper drip rate. Every so often they will need to be adjusted again. Setting up the valves is sorta like bleeding the brake lines in a car... any air in the system at all and it stops working properly. Never let the bucket run dry or you'll need to reset the entire system again.
Mr C is right; finding proper elevation for gravity feed is key. I would add that keeping the feed hose connecting all the carrots as level as possible helps ensure an even rate of drip for each plant. I had to use wire ties to manage the water feed line. Every so often you may need to refill the carrots if they dry out. When set up correctly the carrots provide both passive moisture to the roots and helps control the rate of drip.
