What’s the proper was to hang a valance at the top of this window in the kitchen between cabinets? Will have horizontal blinds it covers. Tile backsplash runs up to the top of the cabinets. Window width is 35” including the 1/4 round that acts as the trim. About 4.5” on either side to the cabinets. Should the valance span to the cabinets or is that too far outside the edge of the window? Keep it about 2” outside the window trim? I’m having a difficult time finding the “proper” way to set that up given my seemingly abnormal setup.
Valances usually sit on a couple of beefy L-brackets that are double screwed into the wall (preferably at wall studs or window header). Once the L-brackets are solid you literally just slide the valance with installed curtain or drape assembly onto them to then install a single screw through the top of the 'L'... so the valance can't slide off.
As far as width of the valance goes, it's up to you. I prefer the curtains/drapes to dictate the width and have them withdraw into their own pockets to pull back to the trim (maybe 2-inches in your case, depending upon hardware stacking). So, you don't have to fight them for tilt-in glass cleaning.