I've read on various threads that 30 mg perfectly vaped and held for 20 seconds is an almost sure breakthrough for most people.

Nearly every time I vape 30 I have a sub breakthrough trip, very anti climactic. Light body load and some mild visual distortion. I am vaping correctly, GVG, torch lighter, one slow steady toke cleared and held for 20 seconds. Sometimes 35 will get me there, sometimes not. For a sure thing I load 40 or 45.

I am wondering if the methadone has something to do with it? I take 120 mg daily and have been for years.

Do any of you have trouble breaking through on 30 mg? I cannot be the only one. What is your breakthrough dose?

Depends, there are breakthroughs and there are brakethroughs

For me anything above 20-22mg could be this, travels - almost every time.
Sweet spot was at 25-27g.
Anything above that almost certainly guaranteed either blackout or unforgettable experience.

Yep that's right on with what I keep hearing/reading. Thanks exit.

Is there anyone else out there who seems to need a little more?

^^ there are people who are locked out no matter how much they smoke, there are threads about it. Just saying what a wide scope there is amongst people. I think I'm quite in line with the standard:
20 chest wetting
25 knee deep bathing
30 diving