OK, after reading all of the high cost rules I thought of a scereo that I do not believe is addressed by anything (except logic). Lets say you do first mortgages that are amortized by one rate and mature in another. Example, the payments are based on a 15 year amortization and the loan matures in 5 years. I am assuming you would use the 5 year comparable loan transaction instead of the 15. Any thoughts?

HOEPA uses maturity date. I am assuming this is the standard for "high cost" maturity as well.

(i) The annual percentage rate at consummation will exceed by more than 8 percentage points for first-lien loans, or by more than 10 percentage points for subordinate-lien loans, the yield on Treasury securities having comparable periods of maturity to the loan maturity as of the fifteenth day of the month immediately preceding the month in which the application for the extension of credit is received by the creditor; or

Amortization is never used in HOEPA or HPML. Length to maturity is all that matters.