You should be able to get 18-19% abv from that yeast compound.
I use a very similar Harris Super Yeast Compound and have fermented from a net 1.150 down to 1.000 giving 20%. The trick is not to throw all the sugar in from day one but to keep feeding the yeasties when it looks like they are nearly done. In other words, go from 1.120 down to 1.000 then feed another 10 points in syrup, then when it's back to 1.000 add another 10, then another 10. When they do turn up their toes and say âwe quitâ you're not going to be left with a super-sweet wine.
However, I make most of my wines at 12-14% and only push it for something like a carrot whisky.