[Mesorah] Vowels under YKVK

[Richard Wolpoe via Mesorah]

I was chatting about Ha'azinu's HaLAdY and its Vowels

OK 
When YKVK is Read ADNY the first letter takes a Sheva
This "seem"s to represent the HATAF patach for ADNY

Yet when it is pronounced Elokim
The Yud gets a HATAF segol and not just a "sheva"

EG See Tehillim 140:8 Elokim (YKVK) ADNY

Why isn't the vowel under the Yud consistently with or without a hataf?