You cannot apply for Retail as well as HNI category for an IPO at a same time. If the retail applicant investor applies HNI category which is for more than Rs 2,00,000 of shares, they are automatically considered as HNI or High Networth Individuals. If a issuer company offered discount to the retail investor, he will not be able to use it in HNI in NII Category.
Moreover, the allotment is always done in a unique manner as the NII receive share allotment in a cognizant basis in the time of oversubscription. For instance, if the IPO is oversubscribed by 100 times, the applicant will surely get one share for each 100 shares.
Whereas if he had applied in retail category, minimum one lot is allocated to the applicant, irrespective to how many shares he applied for. The retail investors (RII) are alloted a minimum of 35% of the total issue size in the Book Build IPOs. The NII have 15 percent of the shares and the other 50 percent is reserved for Qualified Institutional buyers (QIB).