Uneven feed is due to friction losses in the hose. If the hose from the right tank is longer than the hose from the left tank it is going to generate more friction losses which are very easy to calculate. Also not flying perfectly level will have an effect, if you are right wing down then you are probably going to use more from the left wing and vice versa because the higher tank will effectively have more head in the fuel flow will find the easiest route.
Friction losses are significant in small tubes over any distance, an example most people can understand as the water pressure at the tap comes out screaming but at the end of the 10 m hose it is nowhere near the same pressure, this my friends is friction loss.
From the Google
Multiply the length of the pipe L with the volumetric flow rate Q raised to the power 1.852.
Divide this by the pipe diameter D raised to the power 4.87.
Divide this by pipe roughness coefficient C raised to the power 1.852.
If all dimensions are in metric units, multiply the result from Step 3 by 10.67 to get the frictional head loss. If you're using imperial units, multiply by 4.52 instead.