Tried your specs (except still with Tequila) and Simon's specs and I marginally preferred yours, but I think I would split the difference and up the Elderflower to 25ml.
Either way, this is the first St Germain cocktail I've had where the elderflower hasn't completely overpowered everything else.
Used mezcal instead of tequila.
20 ml Suze and Elderflower liqueur - tastes more balanced. And boozy :)