Then there's the keep praying over and over till there's a manifestation of the answer. This is also supported by the words of Jesus in Luke 18: 1-8.
Concerning prayer, I believe that passages such Mark 11:23-24 are true when you know you are praying in the will of God and/or have an inner witness that your prayer has been answered. In such circumstances we can stop asking and start thanking even if we haven't seen the answer just yet. But passages like Mark 11:23 are not ones that can be taken as some kind of magic formula to get whatever we like (as the prosperity name it - claim it, blab it - grab it, teachers would tell us.) It should be weighed up with other scriptures in the New Testament such as:Jas 4:3 You ask and do not receive, because you ask with wrong motives, so that you may spend it on your pleasures.
1Jn 5:14-15 This is the confidence which we have before Him, that, if we ask anything according to His will, He hears us. (15)And if we know that He hears us in whatever we ask, we know that we have the requests which we have asked from Him
So in the cases that 1 John 5:14-15 talks about, where we know we have prayed according to the will of God, then we have confidence that we have the request we ask of Him. And thus can then simply thank him. Yet in the cases that James talks about where we ask with wrong motives, motives of self gain and our own prosperity/pleasure, we shouldn't think that we will receive anything in such cases.
What about when we don't know and haven't heard an answer? Keep praying as Jesus' other parables that you mentioned tell us to. Keep knocking. By nature, most of us aren't very patient. God wants to teach us persistence and patience, and prayer is one way in which He does this. I have something I have been praying about for 20 years. Some people pray for loved ones that don't know the Lord for many decades. Keep going!
As an example, Paul, as you know, once had what he called a thorn in the flesh. He prayed to God that it would be removed. It wasn't and he didn't hear an answer so he prayed again. Again nothing. So he prayed again. On the third time the Lord spoke saying 'My grace is sufficient for you, for my power is made perfect in weakness'. (2 Cor 12:7-10) Once he had God's answer he didn't keep praying. So we see that he didn't just do what Mark 11:23-24 says because he didn't know what God's will was concerning this. So he kept praying till he did know. But nor did he keep requesting the same thing again once an answer came. Though he probably, in his natural self, didn't like the answer (in that the thorn wasn't going to be removed), yet he then submitted himself unto God's eternal wisdom and care knowing that the Lord of the universe will do what is right.
Hope this helps, all the best.