Darkout had an interesting idea, and you should implent it too. When you mine for 9 blocks, mining speed should be the same, but if you mine single block - speed should be 9 times faster. So, increase overall base mining damage and divide it on the number of blocks being mined at the same time.
The mining right now is rather unintuitive, and basing the mining speed on the amount of blocks mined would help a great deal.
