Exactly!
Engines run best when at operating temperature.
The reason engines get better mpg on long runs is because they are usually on motorways so less changing gears , less stop start and generally better average speeds the ideal speed being around 56mph, although that last part was based on cars from years ago so that may be a little different, that is the reason for better mpg not so much the cold engine part although that has some bearing on it but most cars are at operating temperature within ten minutes of driving, sitting with the car at idle it will take longer than ten minutes and all your doing is burning away you fuel.
As has been said before and from what you keep posting, you could learn a hell of a lot from this group judging by some of your posts, your not loosing the plot you just need to get off the 100mph train, slow down, take on advice and learn what's best from a field of knowledge and old age experience that is on this forum