An oddity in sentencing discretion for attempts to commit rape?

The reform of India's rape law in the wake of the Verma Committee Report led to an overhauling of how the core of the offence was defined. It also led to a recognition of fresh kinds of aggravated forms of the rape offence depending on various circumstances, with varying punishment schemes in place to properly sentence offenders for such crimes. 

One such example is Section 376(3) of the Indian Penal Code 1860, which states that:

"Whoever, commits rape on a woman under sixteen years of age shall be punished with rigorous imprisonment for a term which shall not be less than twenty years, but which may extend to imprisonment for life, which shall mean imprisonment for the remainder of that person's natural life, and shall also be liable to fine ..." [Emphasis supplied]

So, there is a mandatory minimum of twenty years in prison for committing rape on a woman below the age of sixteen years, and the maximum possible sentence is that of life imprisonment.

The insertion of a mandatory minimum punishment in any kind of offence has been the subject of intense debate and scrutiny across the globe. What I am interested in here is not that debate, but the peculiar set of consequences that clauses such as Section 376(3) have when considered from the prism of attempts to commit crimes.

Section 376 does not separately punish attempts to commit rape. Therefore, resort must be had to Section 511 of the Penal Code, which states that:

"Whoever attempts to commit an offence punishable by this Code with imprisonment for life or imprisonment, or to cause such an offence to be committed, and in such attempt does any act towards the commission of the offence, shall, where no express provision is made by this Code for the punishment of such attempt, be punished with imprisonment of any description provided for the offence, for a term which may extend to one-half of the imprisonment for life or, as the case may be, one-half of the longest term of imprisonment provided for that offence, or with such fine as is provided for the offence, or with both." [Emphasis supplied]

If you are wondering how do you calculate one-half of life imprisonment, look no further than Section 57 of the Penal Code, which states that for calculating fractions of punishment, life imprisonment shall be reckoned as equivalent to imprisonment for twenty years.  

This poses an interesting quandary for cases where the allegation is an attempt to commit offences such as Section 376(3) [or, for that matter, Section 4(2) of the Protection of Children from Sexual Offences Act 2012]. Reading Section 376(3) with 511 confers the judge with discretion to convict someone for a term which may extend to one-half of twenty years, so theoretically a figure anywhere between 0 to 10 years in prison. But, because Section 376(3) carries a mandatory minimum term of twenty years imprisonment, conferring any sentence below one-half of that prescribed limit would, technically, offend that mandatory minimum. 

Effectively, then, does the judge have any discretion to award a sentence other than ten years in prison for attempts to commit the offence under Section 376(3) IPC, no matter how different they all might be? If we read Section 376(3) IPC read with the attempt clause in this manner which eliminates all possibility of sentencing discretion, then would it not fall foul of the rule laid down by the Supreme Court in Mithu [AIR 1983 SC 473] that vesting discretion with the judge is what makes sentencing just, fair and reasonable from the perspective of Articles 14 and 21 of the Constitution?

If anyone can point to more discussion on this then that will be great!