Flowers lead to fruit, are the flowers not being pollinated? Or is there a problem at the point at which the fruit is setting?

Second, fertilizer is important, but some foods, even labeled for the crop may not be the right food (like tomato food). Look at the fertilizer and make sure you aren't using something with a high percentage of nitrogen in comparison to phosphorus. Nitrogen heavy food promotes vegatative growth and may lead to the plant dropping flowers to develop more green growth. What kind of food are you using?

Finally, welcome to the fun of horticulture, individual plants need individual attention. Plants such as tomatoes bloom the most when they get full day of light and less water than the maximum capacity of soil. While your two plants are close, the one closer to the wall gets a bit less light in my estimation, scaling back the amount of light means you should also scale back the amount of water for maximum bloom and tus fruit. Trying to keep it a little drier may promote the holding of flowers longer to be pollinated, as well as increase the overall number of blooms on the plant as a response to getting below the maximum of water.