Having a DD with a rare genetic disease, I gave up trying to figure out insurance.
For example, our DD needed to have some parts on her wheelchair replaced. The medical supply company sent a quote to the insurance. They denied all of it because the plan doesn't cover repairs. They did say that since the chair was over 3 years old, they would cover a new chair. I explained to them that since DD doesn't grow very fast, there's still plenty of growth left in the chair and we just needed new tires, anti-tip bars and a few other pieces. The total was a few hundred dollars.
The answer I got from the manager of benefits at the union was "We don't pay what's cost effective. We pay what the plan covers". So instead of paying a few hundred dollars, they paid over $8,000 for a new chair.

We had already met our yearly out of pocket so there was no cost to us.
Another example is that they don't cover any immunizations after 2 years old. We got letters of medical necessity from my DD's doctors explaining that the disease has weakened her immune system and that she needs to get a flu shot yearly as well as the Prevnar, Pneumo Vax... They denied it saying that if she got sick they will cover the bills but that they will not cover the shots to prevent them.
I could go on and on but these are just two examples.
I should add that the insurance is self-funded and there are always articles in the union newsletter about how members could help keep costs down.