What you are calling a valence, is actually called a light rail. Most are minimal, and don’t require higher cabinets. But, post pictures for help.

Here are ours:

Editing to add a pic of the underside of the cab, showing the light in back of the light rail:

Photos of your kitchen and the undersides of the cabinets would help. Led tape lights by themselves are only 3/16” thick, in an aluminum diffuser they are 3/8”

You could install LED tape lights in a flush-mount channel embedded in the undersides of the cabinets.