I'll try to make it a bit more clear - but bear in mind I am new to fantasy other than tolkein and lewis so I am limited with the examples I can give.
I have just finished the excellent gray mouser book swords against death and whilst I did like the interaction between the two and I will read more it did seem like many of the stories were lazy and just expecting too much suspension of belief. Now Tolkein has a world full og magic but it wa still damned hard to get out of mirkwood in the hobbit and the the two towers try as they might the fellowship could not catch the orcs after they had taken the two hobbits.
I want to read good fantasy but I want an author that strictly sets out rules within that world that cannot be played around with so the author can get out of a tight spot. I go back again to the Le Guin example when faced with a dragon I was lapping up the pages in anticipation to see how the character ( who's name evades me ) would handle this situation. As it happened he simply changed into a dragon. Anti climax wasn't in it. I did finish the book though and will try her again.
hope that's more clear though I suspect it might not be.
Thanks for the clarification. (Though I can't say I agree with you at all about Leiber on this one. The man tended to be a meticulous craftsman, and the magic in his fantasies does indeed follow certain rules; he loathed the deus-ex-machina and even poignarded it in one of the Fafhrd-and-Mouser tales, "The Sadness of the Executioner".)
If you're looking for that sort of explicitly structured set-up, you may want to look at some of Jack Vance's fantasy, especially the tales of his Dying Earth cycle. There are very strict rules where the use (or even the ability to use) spells is concerned; several of the stories use this as a plot point, in fact. Also, the earlier Witch World tales by Andre Norton pay close attention to this, and keep the magic to a more subtle level as well. (Leiber does sometimes pull out all the stops in his more whimsical tales in the series, such as "Bazaar of the Bizarre", for instance. In these tales, at least, he is focusing on irony or outright farce. He still "plays by the rules", but he does so for a different effect.)
And, of course, for sheer density of realism, you can't get much more of that than with Peake's Titus books (
Titus Groan,
Gormenghast,
Titus Alone). You can literally feel the oppressive presence of Gormenghast all around you there. Then again, there really isn't any "magic" in those books... though there is in the single short tale featuring Titus, "Boy in Darkness"....)
As I said earlier, you might want to take a look at some of the older writers in the field, as the approach there toward such things as magic was often quite different....