^ True but the actual Center of gravity COG isn't really at the heartline either. It should be a little lower than the HL, not sure about inverted coasters though but different trains should have different cog lines for the physics to be more realistic.
Civil and mechanical engineers also rely on approximations for any calculated outcome depending on the situation. COG might be a little lower if a bunch of fat asses are riding or a little off to the side if the one side of the train is loaded heavier. aka y= >value1, < value2 x= > value3 < value4 under the limited conditions aka no one over 150 KG to ride etc...
BTW I only saw the 06 June update now on
http://nolimitscoaster.de of the new support beams. Afraid I'll have to upgrade my PC. lol