Why isn't the English channel a strait? Calais can be seen from southern Kent on a good day, and the straits are actually narrower than the Straits of Gibraltar (which were a strait in Vanilla EU 3). The only thing that has made the channel a barrier historically is the power of the English navy. Making the channel a strait would make sense gameplay-wise as well. Holding Calais would suddenly become much more important, rather than just being kind of useless like it is now.
I also support making Gibraltar a strait as well, because of the strategic depth it gave to holding Ceuta.
I also support making Gibraltar a strait as well, because of the strategic depth it gave to holding Ceuta.