For some reason not able to respond on Carol’s thread so hope this works …
I’m 77 years young with many years of bluebirding experience … not in my backyard, but on my Bluebird Trail and that of others. Yours is a “gable” roof (not a V). It’s NOT an approved EABL nest box design in part for the very reason you’ve stated – “The box has a v-shaped roof which makes it impossible to put a wren shield on the box.”
You wouldn’t find any member of a state’s Bluebird Recovery Program ever recommending your WRU gable roof bird house design for bluebirds … https://imgur.com/H16QYiZ … in part for the very reason you’ve stated.
My advice is the same that you’d receive from members of any state Bluebird Recovery Program … “Use an approved EABL nest box design!” If you consider my post “rude” it’s unfortunate. If Salis had their way they would tell WRU not to promote your bluebird house as a “nest box” for the very fact that it has a gable roof not a flat roof.