Right that makes sense.  The value of your mBTC is falling relative to the value of MAC.

So the 0.00679 mBTC you earned when the value of MAC was likely at 0.00679/3.492684 = 0.00194 is now only worth 0.00679/0.00270 = 2.5148MAC

You mined the coins when their value was low and now the price has risen so that value is worth less than it was before.

You don't mine specific coins on Zpool you mine the value of an algorithm at a particular point in time and get credit for that value in mBTC.  You then get paid out the coin you select in the c=XXX statement based on the value of that coin relative to mBTC.

If the price of MAC had fallen after you mined them you would be getting more MAC than you originally would have mined up.  This is why multi-algo miners work well on zpool because you mine up the most value at the time that the miner is mining.

Maybe there should be a way to mine coins directly, but at this point there is an internal exchange to mBTC at the time you mine the coin.  I think this is about the only way that you can do it when you can be mining against several coins at once on a given algorithm based pool.