Rough guidelines for glycerine ratio

[Liqueur Lover]

Hi all

I apologize if this question is borderline stoopid, but I am wondering if there is a general amount of glycerine that people use as a starting point to add to homemade liqueur. Of course I realize that one could add slowly until the right consistency is reached, but it would also be nice if there were a known baseline to start with or a standard amount that people use. This would save me time in having to experiment upward.

I made a blueberry liqueur that is "resting" right now and I can tell it can use a little body, but I don't want to overdo it or underdo it (although If I underdo it that can be adjusted obviously).

I have what looks like about a liter of liqueur... what would be a good starting point, if anyone knows? 10 mL per liter? 25? I tend to like my liqueur on the thicker, sweeter side (yet still 24-28% abv). Chartreuse, for example, is a perfect consistency for my taste.

Thanks for any info.