Retro Pay / Monthly Entitlement Amount

[Sharm]

I recently received my decision letter from the VA for obstructive sleep apnea, which was currently 0 percent disabling, increased to 50 percent effective June 19, 2107. I submitted via e-benefits the intent to file on June 19, 2017, and actually complete the claim for decision on May 8, 2018 (within the one year time frame). The time that I submitted the completed claim (8 May 2018) to the rating decision (20 July 2018) was 100 days, which seem pretty good time to me. My combined rating evaluation was 30% (effective 2010) and was increased to 60% (effective 19 June 2017).

My monthly entitlement amount is shown below:

 

How is retro pay calculated?  Will I be back pay the $1,180.13 per month from the effective date of 17 June 2017, or only a portion of it as I was paid by the VA for the 30% (with $512.51 being deducted from my military retirement). Will I get the other portion back from DFAS from my military pay? I don't understand the math.

 

Many thanks in advance for your replies.