I have this too, in the summer, once the cover is up.
No answer, only tips:
make nest boxes more attractive, clean, extra straw, etc?
Find nests outside and collect eggs from them.
Or provide dedicated nesting shed as well as their hen house?
Mine loved laying in a couple of fruit boxes on the top shelf of an old wardrobe last year (it's under a roof), it worked fine, quite happy for this to happen again this year if they choose it again.