Cocoa Butter and Melting Chocolate
Cocoa butter is a very important part of all real chocolate. In fact chocolate isn't chocolate unless cocoa butter is a significant portion of all the ingredients. Real chocolate uses cocoa butter instead of non cocoa bean vegetable fats (palm oils typically) like what are found in confectioner's coating (aka: meltys, a'peels, melting chocolate, dipping chocolate, pre-tempered chocolate etc).
Cocoa butter is the naturally occurring fat in cocoa beans. Therefore it is a critical part of all chocolate and typically it compromises half (50%) of the total cocoa solids in couverture chocolate.
Basically cocoa butter melts at 98F but this varies depending on the type of cocoa butter. For example cocoa butters from cocoa beans grown at the Equator have a higher melt point then cocoa beans grown at higher latitudes like 20 degrees North or South. The higher the latitude the softer and lower melt point of the cocoa butter. This is due to the number of hot daylight hours the cocoa trees are exposed to within a 24 hour period during the cocoa growing season.
Our Belgian chocolates for example have a high quality cocoa butter from Malaysia (on the Equator) in them and as a result the melt point is higher and the temper will be more solid. Our Organic Chocolates on the other hand come from Peru further North of the Equator and as a result, this chocolate has a lower melt point and softer cocoa butter. One type of cocoa butter is not better then another type, but typically the higher melt point of cocoa butter will offer a greater range of tempering temperatures while lower melt point cocoa butter has a slimmer margin of error when tempering.
I hope this clarifies why some chocolates with the exact same cocoa percentage seem harder then others (Organic Dark 70 versus Belgian 64). It is due to the cocoa butter type we use in formulating them.