If the loan is subject to Reg Z, regardless of whether it is an HPML, you would report rate spread. Please see the information from the regulation and HMDA guide, below.
1003.4(a)(12)(i) states: “For originated loans subject to Regulation Z, 12 CFR part 1026, the difference between the loan’s annual percentage rate (APR) and the average prime offer rate for a comparable transaction as of the date the interest rate is set, if that difference is equal to or greater than 1.5 percentage points for loans secured by a first lien on a dwelling, or equal to or greater than 3.5 percentage points for loans secured by a subordinate lien on a dwelling.”
Effective January 1, 2018 this part reads: “For covered loans subject to Regulation Z, 12 CFR part 1026, other than assumptions, purchased covered loans, and reverse mortgages, the difference between the covered loan’s annual percentage rate and the average prime offer rate for a comparable transaction as of the date the interest rate is set.”
Also when looking at the Guide to HMDA Getting it Right it discusses when and what to disclose on p. A-8: https://www.ffiec.gov/hmda/pdf/2013guide.pdf