To get melted puddles with irregular shapes like in these photos, use chopped chocolate from a bar with over 70% cocoa solids. The darker the better when it comes to meltiness because the higher the total cocoa content, the more cocoa butter it will have and that high fat content is what makes chocolate melt and spread easier. Also, block chocolate is tempered as a block that you will break up and expose all sorts of jagged edges whereas chips are tempered in a specific shape that will stay in place.