ruku3 means to bow and includes sujood and when you fall down into sujood. If someone wants to rest at his knees before falling to his face, then I see no harm in that. Falling to the chins (adh-qaan) is an expression according to Lisaanul-Arab and other lexicons that just means prostrating with your head to the ground (not actually on your chin because the expression is taken from camels when they put their faces to the ground they can only fall to their chins).
As far as the claimed 'middle prayer' it says al-salaatul-wustaa. it is not an idaafah as in salaatul-wustaa. al-wustaa also does not mean noon or afternoon. This is a common misconception. If God says 'the middle prayer' that has to refer to a prayer already mentioned that is the 2nd of three. but God mentions salaatul-fajr and 'eshaa and mentions the noonday (dhaheerah) but no noon or afternoon prayer. wusta means moderate and best. Understanding it as 'middle prayer' would be like if it said 'and the 9th prayer.' Well, there is no 9th prayer ever mentioned in any other place in the Quran. So that doesn't make any sense. And there is no middle prayer mentioned at any other place in the Quran, only fajr and 'eeshaa whose times are clarified as the edges of daylight hours, being around sunrise and sundown and the times right after it during the night, being twilight and the parts of the night still close to sunrise and sundown. Praying in addition to the two obligatory times is not wrong, but there is no noon or mid day prayer...just noon and afternoon praise. 30:17-18 fa subhaana llahi heena tumsoona wa heena tusbihoona wa lahu al-hamdu fee-s-samawaati wal-ardi 3asheeya-w-wa heena tudh-hiroon
Prayer is truly just standing (qiyaam) calling on God, praising and reciting the Quran and prostration (sujood). 25-65: walladheena yabeetoona lirrabbihim sujjada-w-wa qiyaama However, so you know ruku3 is sujood and sujood is rukoo3. See lisaanul-3arab and mu3jam alfaadhil-qur'aan
baata means 'to be' or 'to become' as well as 'to spend/stay the night.' sahar is actually to stay up throughout the night.
And the way of those whom God bless among the prophets (19:58) idhaa yutlaa 3alayhim aayaatu-r-rahmaan kharroo sujjada-w-wa bukeeyya
17:107: min qablihi idhaa yutlaa 3alayhim yakhirroona lil-adh-qaani sujjada
(understand qablihi as 'before it' in the sense of 'in its presence')
And as you know we are given many examples of how to pray from Mary to Zachariah (sallaa allahu 3alayhimaa wa sallam)
btw i beileve that As-salaatul-wustaa in the Quran actually refers to 17:110 laa tajhar bisalaatika wa laa tukhaafit bihaa wabtaghi baina dhaalika sabeela
But if you want to actually pray during these times. I see no harm as prayer at any time brings you closer to your lord.