a good way of thinking about 'rhumb lines' vs 'great circles' is to think of the earth as an orange. If you slice the orange through the middle and get 2 equal halves then you sliced a great circle. If you don't slice through the middle and get one big bit and one smaller bit then you sliced a rhumb line....it doesn't matter what angle...or where on the orange you slice...the principle is the same.