They ARE too low and too small. If you can't find lights that have a low base and then extend up, you'll have to change the position of the boxes.

This fixture illustrates my suggestion of the fixture that has a box attachment at the bottom and then extends up from there.

Personally, while the size could be bigger, they would be acceptable up TWO feet higher.

I'd change them out to an enclosed down light... better lighting for a walkway, limited light pollution, and no glare at eye level. https://www.lampsplus.com/products/kichler-harper-7-inch-high-black-outdoor-wall-light__44h77.html

Oh these are all great suggestions- thank you!!