I usually either just put them vertically in the back corners or horizontally near the top directly below a filter return. Hardly noticeable and they heat my water just fine. I've never kept my heaters near the bottom or at a 45 degree angle. I think that suggestion is fine, but by no means is it an absolute requirement. Put your heaters where you want. The most important thing is to have good water flow around them to carry away and disperse the heat.