Aggregate Turnover more then 5 Crore: 6 Digit HSN code shall be mentioned mandatory on Tax Invoice.
Aggregate Turnover less then 5 crore : 4Digit HSN code shall be mentioned for B2B supply in Tax invoice.
Hence from above it's being very clear that Reporting HSN is in Tax Invoice & the particular in tax invoice need to be mentioned as accordingly in GSTR 1.
So in my view the Registered person whose turnover is below 5 crore is not required to provide HSN for B2C supply in Table 13 of GSTR 1