I have been attempting this DIY thing for the past month or so and although my mixes come out nice and I always finish them I will say that they never seem to be as good as the ones you buy off the shelf. I have a few different flavours to play with but I must say I am struggling to find recipes for the ones I have. Like I search the recipe sites and I think something is really cool only to discover I am missing some of the ingredients. So far I have nailed menthol mixes.
Blueberry Ice
TFA Blueberry 7%
Just B Menthol Ice 10%
All I'm going to say is additives I can tell you that Ethyl Maltol (sp) helps A LOT when it comes to making your flavours pop and shine through a mix. Also, you may want to start upping your flavour percentages if you're making a VG heavy juice.