actually you can have rough computation on how much you can earn daily after the block halving, just divide to 2 how much you are getting per block found and you will still have some small profit out of it
Yes that what i am saying if you current you getting 10 usd daily then after Havel you will get $5 approx ..as current the efficiency is around 40% so after Havel it may be almost 70% so you have quite low profit and reward is less maintenance is high
It has other factors as well. Say that the site begins to find double the amount of blocks due to miner drop out else where, then profits can stay the same. To state that it will be just cut in half due to half the overall block payout is negating the other factors involved.