I don't know why the both of you are complicating things for yourselves. But let me try and explain this as simple as I can so you guys can get something right. When an investor get his salary and he removes all the money for family necessities, what he have left is called discretionary income. From that discretionary income he can remove a portion of it to build his emergency funds and his reserved funds. Then he can invest the rest in bitcoin. As times goes on, if the investor sees an opportunity in the market and his salary hasn't come and he doesn't want to miss such an opportunity, he can take money from his reserved funds account to invest in bitcoin and build it back gradually. So yes an investor can buy bitcoin with money from his reserved funds account.
However, I'm still not very confident about using reserve funds to invest in Bitcoin. While it's true that reserve funds are quite flexible and aren't used for emergencies, I personally feel more comfortable investing using only discretionary funds. Because discretionary funds are funds that will not be used for any other purpose.
It's not like am telling you to always turn on your reserved funds every time to buy bitcoin. If you go through my previous post you will understand the instances or circumstances which I said you can turn on your reserved funds to buy bitcoin. This should only happen on special cases where you see an opportunity in the market which you wouldn't want to miss and at that time, your discrictionary income has been exhausted on your previous purchases and you are waiting for your next salary which is not yet due to be paid. (Or your salary is being delayed) In situations like this you can use part of your reserved funds to buy bitcoin. If you didn't know this before, perhaps you just learnt a new thing.