εστι(ν) with "dative of possessor"

(My understanding, based on a recent discussion here, is that “dative of possessor” is a misnomer; hence quotation marks)
Dickey has two sentences:
a. τούτῳ ἔστι μείζων οἶκος ἢ ἐκείνῃ. (p. 138)
b. τούτῳ ἐστὶν γενναιότερος πατὴρ ἢ ταύτῃ (p. 239)
I have two questions.

  1. Why is εστι(ν) accented differently in these two cases? Is one of these two versions more proper than the other? If so, which one and why?
  2. Why is movable ν retained before the consonant γ in (b)? I failed to find a rule to this effect.
    Thanks in advance for your help.

a) seems to be wrong; according to LSJ ”with the dat., ἐστί μοι I have, freq. in Hom., etc.”

However:
Smyth 187b. ἐστί is written ἔστι at the beginning of a sentence; when it expresses existence or possibility; when it follows οὐκ, μή, εἰ, ὡς, καί, ἀλλά (or ἀλλ᾽), τοῦτο (or τοῦτ᾽); and in ἔστιν οἵ some, ἔστιν ὅτε sometimes. Thus, εἰ ἔστιν οὕτως if it is so, τοῦτο δ ἔστι that which exists.

A dative of possesion does, in a way, express existence, so I wonder if this distinction reflects actual practice or whether it’s just an academic convention. At any rate, Dickey’s mistake is understandable.