Struggling with final booster stage TWR
I’ve built a payload intended to take a scientist to Minmus Orbit to collect high and low space science -
Goo, Baro, Temp, Materials Bay and EVA Science project. Just one of everything that he’ll reset and collect while orbiting. With the command module, two bays, a small battery small reaction wheel the science bay, a Terrier engine, and fuel capacity for the vacuum Delta V to inject from LKO to Minmus and back home.
I am having a lot of trouble, without copying YouTube videos (so something must not have “sunk in” for me on all the ones I’ve worked through so far) figuring out a way to get this payload with approximately 2+ TWR on my third booster stage. The series I have been watching have recommended approx 1.33-1.5 TWR for pad liftoff, 2.0 for second stage and 2.1-2.2 for final stage. But fuel and engine combos just aren’t getting me there (whether on Vacuum or sea/atmospheric setting). I thought usually we wanted a Swivel engine as the final stage because of the gimballing, but It just can’t get me to that thrust to weight ratio. What am I missing?