I don't understand why it is a problem that the hp of a wreck is correlated to the hp of the base unit instead of it's mass value. Right now you know that the damage of a bomber run or whatever other weapon that is sufficient to kill the target is also sufficient to kill the wreck. In my opinion it doesn't get any more intuitive than that.
Other people have already outlined that there are edge cases where the hp/mass varies so much that I doubt the new system would work without making it complicated.
The only thing I would like to see is having the hp of reclaim correlated to the reclaim value as these don't have any straightforward way to know the hp and it is a bit ridiculous that big solid rocks die to a single bomber in the first pass.