There is no fixed monthly income in trading, to say that first, its hard to predict market and to have profit all the time, even harder to always have same high profit. Bitcoin and trading are two different worlds, trading is gambling and its full with surprises, you really need to be an expert to constantly generate profit, on other hand just buying and holding bitcoins can generate good profit with less risk. Bitcoin trading is capable of supporting traders to earn a living out of it still aiming for fixed income seem is not appropriate as per the nature of results we may expect on daily basis
Yes, I saw that there is a possibility to have a fixed income in trading but not in the fixed amount of earnings in bitcoin. Because how can you have the fix amount if the motion or movement of the coins is from time to time it changing. Meaning, the volatility of bitcoin and altcoins is not fix due to when the value react the traders take action at once