Concertina ladder install

Hi

first post.

Concertina ladder installation where ladder board (pic below) is 200mm but joists to attach to are not near that height

I saw on an old post I could build up the joist so that it’s 200mm but wondering if I could attach it to joist and the top screws to the two supporting beams- basically securing the ladder board over the connection plate and securing with screws at the corners

What are thoughts? Doing it by building up the joists I’m worried it may be a bit heavy. Am I worrying about nothing?

if not going over connection plate then I’d build up this so it’s 200mm high

Build up , weight gain negligible.