The base defense defines how many rams are needed to drop the wall bonus. The hit points define how many rams are needed to drop the wall level. Modifiers affect in both cases.But that formula is a correlation between the wall level and the base defense. It has nothing to do with the hitpoints. There might be a correlation there but I don't know which... If you can take that formula and get the hitpoints of the wall that you see in the wiki, I will believe what you are saying.
Also can you explain me the math of your calculation for the two reports I quoted up there...