How many times should the tongue strike the roof of the mouth for the pronunciation of the letter "Rāʾ" to be considered correct, and what is meant by "al-raʿdah" (the tremor) in this context?

The articulation point of the letter "Rāʾ" is not the roof of the mouth. Rather, it emerges from the tip of the tongue, slightly inclined towards the back of the tongue, alongside what aligns with it from the upper teeth. Striking the tongue against the roof of the mouth does not lead to the correct pronunciation of the "Rāʾ".