Тем больше - incorrectly. correctly - Тем Более.

Part II The less bookish and a really common in _speech_: Казался благоприятной перспективой,(!) тем более, что... Note the comma. Here 'тем более, что' got lexicalized (likely it has developed from the above usages!). It means 'all the more so', 'especicially given that'. It acts as an adverb. It isn't related to 'outlook', 'favourable', and anything in paricular - it refers to the whole statement and introduces a new one. Now why people suspect a typo in your example and what it means? It implies that the 'favourable perspective' is also big. Both big and favourable. And it is even bigger because of... It is unusual Russian: 1. we don't say 'большая перспектива' normally, but we have an idiomatic 'большие перспективы' (Pl). 2. even this sometimes used in a half-joking way. 3. can an 'outlook' be both big and favourable? It is Extremely rare usage, as both often used just to mean 'nice', 'cool':) The author did not just used a rare constuction: "big, favourable outlook". He doesn't writes it explicitly: He _hides_ the assumption that the perspective is big into 'even bigger':-/ Either this guy got confused with his own language... and he has a thing towards unusual and complex constructons:)

Nao, I meet such a wording mostly in books. It translates as 'all the more'. Now, how it works: Part I "[something] тем интересней, что [a fact]" "....было тем интересней, что" "...казалось ему тем интересней, что..." "...казалось ему тем более интересным, что..." "интересней" = "более интерес[...]". Two ways to form a comparative. By [...] I mean the ending needed (short/full, f/m/n, sg/pl, case). It all means: [smthng] is/seemed interesting. But [the fact] makes it Even More interesting. "Тем" = Inst. of "то", 'that'. "То" refers to [the fact]. Instrumental case because... it one of archaic meanings of Instr.: [the fact] MAKES it 'more interesting', DUE TO [the fact] it gets more interesting. "Это обещало прибыль тем бОльшую, что..." For "большАя" only one comparative form exists: бОльшая. *более большАя - ????:-/ Here 'even more' refers to 'favourable': "Казался перспективой тем более благоприятной..." An inversion is possible (a bit archaic): "Казался перспективой благоприятной тЕм более, что..." (тЕм is stressed sometimes to distiguish from the next one). Here another comparative gets impossible. You can't put 'благоприятней' into here.

"... тем более, что ..." ))