Brewfather - 1 oz of sugar adds 3% ABV?

[fuzzybee]

I'm working on a Belgian Single recipe which has fermentables of Barke Pilsner and cane sugar. I'm tweaking my % levels, and I noticed something weird. I have 9 lb 12 oz Barke Pilsner:

at 7 oz of Cane (Beet) sugar, I get an ABV of 4.6%, OG of 1.043, and FG of 1.008.
at 8 oz of Cane (Beet) sugar, I get an ABV of 4.7%, OG of 1.044, and FG of 1.008
at 9 oz of Cane (Beet) sugar, I get an ABV of 4.7%, OG of 1.044, and FG of 1.008 (same as 8 oz?)
at 10 oz of Cane (Beet) sugar, I get an ABV of 5.0%, OG of 1.045, and FG of 1.007

I understand the rounding of ABV, but the only thing that changes on my style graph from 8oz to 9oz is the BU/GU goes from 0.76 to 0.75

 

[VikeMan]

I don't use Brewfather, but...

In 5 gallons of wort, each ounce of sucrose should add about 0.0921% ABV.

So if you were starting with 5 gallons of wort including 7 oz of sucrose that yielded an ABV of exactly 4.6%, it should go like this (rounded):

w/ 7 oz: 4.6%
w/ 8 oz: 4.7%
w/ 9 oz: 4.8%
w/ 10 oz: 4.9%