Coconut milk ice cream — getting volume?
Try to decrease the fat percentage in the custard. Full fat coconut milk has a fat percentage of ~20%, hence the custard has about the same. Fat tends to make the ice-cream more heavy and "creamy". Ordinary ice-cream usually have a fat percentage around 10-16%, and even lower for gelato type ice-cream. 

To decrease the fat percentage, add some liquid with low-fat.