Bed size?

I now have 3 raised beds 2 of them 6ft wide and 1 3ft wide but against a boundary fence, all have 2ft high sides which saves me having to bend and allows me to reach 3ft easily, the narrower one if I have something like potatoes planted in it, has drier soil possibly due partially to the fence shielding from the rain though the foliage acts as an umbrella shedding the water, in an average year I don't need to water the wider ones as the rain water gets to the soil, in the past I have found that the narrower beds are generally dryer, not a problem if you practice watering anyway, but that is not something I have to do, though last year was an exception (which I hope happens again )