I think depends on 2 main things.
The trim area does not necessary means that you do not touch or put something in this area (like with a photograph).
A side note: Thoose margins are (in my opinion) too small to have text, so that is not a "safe area". In my opinion a safe margin is arround half inch or 12 mm on the outer borders.
If you are using a very, very obvious and clear grid, you probably need to align on the inside of that grid.
If the grid is not that obvious in the finnal design, or you are using a very clean design, probably on the page itself... or something in the middle for a visual correction.
One more things to consider is the type of bound the book will have.
A staple bound can show all the design when 2 pages are wide open. So no need for an inner bigger safe area. That will depend then, on the design.
A sewn binding could not show all, so in that case probably you need some diference on the inner one.
In this particular case you probably need to align inside the grid, with some visual correction if the case needs it.
But it also looks different when the design is on one page or both pages (like a title on a 2 page photo.
The final word
You need to make a choice depending on the design. Print a dummy and test it.