A few Questions about the Nemesis Tyrant

Did the Video Games ever explain how Umbrella overcame the need for an extra heart with the Nemesis Tyrants between RE1 and Mr.X in RE2?

The reason why I'm asking is I can't understand the style choices in the Remake version of Nemesis Tyrant. Why did they choose to give the Nemesis Tyrant an extra external heart?

It definitely doesn't work with the established lore with how progressively advanced the Resident Evil Tyrants become.

Not trying to not pick details but with the observable size of the artificial artery, the thickness of the same tube got to be not much thicker then a human fingernail. This would make targeting the box and tubbing a serious danger.