Hello & welcome to the forum CC
You mention that you have an RC installed. Do you know what your draft is before the RC when you have your coal fire established? What draft is your RC set to maintain? Have you measured the draft with a manometer?
Sometimes it's easier to learn to burn coal with nut size. I'm not familiar with a Saey 92, but the larger size coal reacts a little quicker to changes in the amount of combustion air. Pick up a few bags to try out in your Saey.
You've mentioned burning wood in your Saey. Do you set your air inlets differently when you burn wood vs. coal? As you might have read, coal requires all of the combustion air to be fed at or below the level of the grates. Post your answers and we'll get back to you.