I’d go with a Copa as shown here if you can. https://www.littlesugarsnaps.com/summer-gin-and-tonic-with-elderflower-lemon/ The ratios there seem better to me, but try both and see what you like. St. Germain can be overpowering in larger quantities. A typical “daisy” like build might be 2 oz gin, 0.75 lemon, 0.5 St. Germain. You’re just adding volume with the tonic. Don’t use cheap tonic for this! A Schweppes or Canada Dry type could just overpower it all with sweetness. Fever Tree Elderflower or Light, or one of the Franklin and Sons should work well. (Hmm I remembered the Rosemary one as not having Olives in it. That may not work as well as I thought.) If you must use cheap tonic try cutting it with seltzer until you find a “sonic” mix that works for you!
Thanks for the links, detailed info, and correction on a gin blossom! I'll take these ideas into a tasting session soon, and I'm sure the drink will be better for it ✨