25 will result in enormous dots which won't translate to a nice looking gradient. Ideally you want 22.5 or 67.5 as your angles and the frequency will depend on the mesh you choose, but a frequency of 55 will produce good results and shouldn't be hard to hold on a 230+ mesh (though I often use 45 as I print manually and 55 can be a bear to register depending on the art). The idea behind the 22.5 or 67.5 angle is the mesh is at 0 and 90 degrees, and the knuckles of the mesh are at 45 degrees, so you want to split those angles to prevent having dots fall on threads or knuckles, causing lost detail and moire issues. I won't even go into anything related to film output or things like underbasing and dot gain as others on the forum are much more experienced at that part of it. The angle thing is just simple logic.
