Hi everyone !
First of all, i've search a little to find if my question has such answers but, apprently no. So I post here now 
My question is : Does the copper ore is fairly distributed for layer 10 to 60 ? I mean, is this wanted ?
Because it seems (but I could make a mistake) that we easily find copper around layer 60 but very rarely around layer 15 ... maybe it's due to the vanilla ore distribution : copper, iron and coal are the only ores in layer 60 (so copper will be easily found) but copper has to find a place beetwen diamond, redstone, tin, iron, coal, uranium and lapis in layer 15.
PS: Sorry for my pretty bad english, hope you'll anderstand