I've always done a burnout until I see smoke. When only doing a small burnout it seems they are easier to overpower. The only reason I go through the water is when I'm in my white T with a spool. Much easier to get them spinning when they are wet.
With good track prep, low to mid 20's psi seems best. On cold days, I lower the psi to upper teens.
Your experience with the MTs seem similar to my experience recently with my new trans/converter setup. Now that you have your tune better, you are making power better and its easier to overpower the tires. But you need the rpm to hit the converter and if you leave at too little boost, you are not at enough rpm for the converter and it bogs. Hence 4lb launch it bogs and 8lb launch it spins.
Richening up your tune down low may help you with traction control. Also, tightening up the converter would allow you to leave with less rpm and less boost off the line. Watch your rpm off the line and there may be a magic area between the 4lbs and 7lbs where there will be enough rpm so you don't bog down and not too much where you'll build too much boost and blow the tires away. You might be able to benefit from some kind of launch control/rpm limiter once you find this point if you can't watch it close enough every time.
For me, I'm looking at going to 325/50 MT DRs or some 28x10.5 slicks. I've been 1.4s on 275/60s, but I want to be able to hit it harder and not worry about spinning. I've even got an electronic boost controller with launch control and that doesn't even fix everything to be able to launch where I want it. I'll need to go to a CO2 setup to truly be able to control the launch parameters so that its consistent every time. Its not that easy when you have a narrow launch window where its easy to overpower the tires.
So keep trying and pay attention to your rpms at launch and you might find that sweet spot.