with a whole set of explosion protect 2-3 i get usually only half a heart off

I have also noticed if they explode near a protected door, that door wont be protected anymore.

Yes, that does happen sometimes. Also, for anybody who doesn't know, in the nether and the end, explosion damage (beds and TNT) WILL destroy cprivated/protected furnaces and chests. This means that your little fort in the nether made of cprivated furnaces STILL can be destroyed. (I know that better than anybody... <object class="emojione" data="https://resources.enjin.com/1489581540/themes/core/images/emojione/svg/1f61b.svg?0" type="image/svg+xml" standby=":p">:p</object> Adriedupleaf especially)

hmm I've noticed this problem. It sucks but it makes you learn to wear armor whenever you venture out real quick. Iron is easy to come by so there really is no reason to not have at least that.