Jens, for clarity please explain what is "wide".
Heat will diffuse throughout your Cote de Boeuf according to its thickness, always the smallest dimension. Weight does not matter. Cook the meat without the bones attached, but in a separate package at same time and temperature. Bones can cook longer so they can start first then package your meat and proceed to cook.
Rib bones are solid and nearly inert, thus little to no flavour contribution, but they do suck up a lot of heat energy. Keep them separate. The "finger meat" between the bones has a lot of flavour-rich connective tissue which many cooks mistakenly attribute to the bones.
10 hours will be plenty long.
Please advise on your result, - and thank you.
Feedback is the breakfast of champions.