I don't strongly object to this, but we have to recognize that the concept of "I only need 700 ml" isn't something that your player possesses - and it may not be something we should be optimizing for for this reason.
They know they've been hurt and "lost a lot of blood" - to the point where their faculties are impaired. Yes, the effects do worsen, but do we really think anyone is going to have the ability to gauge the amount they need to put back in to "feel better"?
Seems like a stretch.