Since the achilles tendon attaches to the soleus and gastronemeus muscles that make up the calf, doctors tell us to stretch those muscles. Muscle has the capacity for elongation much more than tendon or ligament does, so that is where one would get the most efficacy. So if the calf is tight, the achilles tendon is tight, and the plantar fascia is tight. If the calf is loose, in theory the rest of this system is loose. Of course, this is all theory because I've stretched like crazy and it doesn't seem to work for me. But I used to do a plantar fascia stretch for a long time and that didn't seem to do much for me.

Night splints ( as I understand them ) are also more for stretching out the calf and achilles tendon than the plantar fascia, although the plantar fascia also gets stretched. I keep running into trouble reinjuring my fascia with these stretches. I was using the prostretch for a few weeks and getting a really good stretch, but I overdid it and my feet felt like they were burning for a few days so I had to stop til it subsided. What a pain. Anyhow, I hope this helps.