First and foremost, props to GrowGoddess, without her blog and this site I would've never even considered e-cigs for cannabis. Thanks to her documented experiences I was also able to make my own tincture using my Super Lemon Haze. I've only done 2 runs so far, but I am a convert for sure. I'm considering replacing my good ol Zong with vaping now...
I think the ratio is more of a personal preference. How often do you wanna clean/replace equipment....how many drag(s) do you want to take to get to your preferred level of medication...things like that will dictate how thick/strong your thc-juice is. Just keep in mind that its easy to keep making the juice thinner/weaker...but unless you have more QWISO readily available you can't add thickness/strength back.
Someone asked if it smells at all? Yes, but with caveats. The smell on exhale is faint...and you can hold in the hit so next to nothing is exhaled, or if you have a variable one dial down the voltage or wattage to produce less vapor to begin with. If your goal is to vape thc-juice virtually undetected you could always buy flavor concentrates to add to your mix, that will mask the exhale. (Personally I LOVE the natural taste the QWISO made from my SLH)