Thought Id chime in here to help out. Ive been vaping DIY VG juices since I started over a year ago and Ill repeat what I have said several times here in the forums... contrary to what some people think VG works in any and all atomizers. When it isnt working in a particular atty its because its still to thick viscosity wise. DW will fix that problem in any and ALL atties.
Now the question is how much DW is too much, or too little, in a VG mix?
The first problem I had to solve was viscosity of VG. In the beginning I was a ego-c user and those are notoriously finnicky with high VG. I went thru weeka of trial and error with mixing, lots of burned hits, ruined attys, you name it. So after realizing it wasnt the equipment, but my juice at fault I set out to find out the right viscosity for VG bases juices.
All of my juice today is 80%VG/20% everything else. Whether that is pg or alc based flavors, or additives like DW, sucralose, em, citric or malic acids, etc. That 20% total is key for me. If I use just one flavor at 14% then I add 6% DW, for example. If your flavoring or other additives are indeed 100% VG also then you will want 70%VG/30% everything else. These ratios for me are never fail.
Now how much is too much DW?
When working with VG base and pg or alc based flavors you can go as far as 65% additives. However this should only be in cases where there is a high amount of flavoring being used. The DW may not even be necessary when flavors are more than 25% of your mix. If you find in these mixes that they are still too thick, a couple drops of dw per 5ml is usually all that would be necessary after the fact and it will not effect flavor.
As to whether or not VG requires more flavoring.... I find that to be a myth and at best the difference is negligable. Ive done tests side by side identical in both PG and VG bases and imo there is no discernable difference to me aside from PG just tasting stale and gross. Im sensitive to pg, cant stand the stale taste of it anyways. To me, any juice with high pg is a ruined juice.