Go easy on the size of the glass you use, or this drink will become over-diluted. Due to the lack of ice in the serving, also ensure the soda is well chilled...
Fiorente recently appeared in our area and my wife just stocked up on Belvoir Farms Sparkling Elderflower Lemonade so used that instead of soda. A big lemon (1 oz/drink) countered the extra sugar of the lemonade. I normally shake & dilute a lot: shake thoroughly, let stand while I ready glasses & garnishes, then shake again before straining every last drop into the glasses (waste not, want not). 4 oz of ingredients yielded just 6 oz after dilution so added a few ice cubes to 10 oz glasses. Good!
Needed more soda, even with just an 8 oz/240ml highball glass. Fill to the brim in such a glass. A decent, if uninteresting fizz with elderflower, juniper and citrus to the fore.