I agree, there isn’t anything in the Reg X force-placed insurance requirements that dictate how you should determine coverage amount like there is in the flood rules. I recommend looking at your loan contract and policy to determine what you are permitted to do. Also, on a second lien, you should ensure you are added to those policies and then follow your loan contract and policy for your coverage amount on junior liens.
Beginning on page 75 of the preamble to the Servicing Rules, 1024.37 and coverage amount are discussed. Here’s the link: https://files.consumerfinance.gov/f/201301_cfpb_final-rule_servicing-respa-preamble.pdf