What version of Tandem pump do you have and how are you currently using it? Do you have a t:slim x2 with CIQ (Control IQ)? Are you currently using C-IQ? (Is it turned on? )
Frankly, I am not sure how one calculates either their bolus carb ratio or their basal rates when C-IQ is active. Turning C-IQ on means it will be adjusting your basal rate and potentially also delivering correction boluses. I don’t know how you tease out the effect of a bolus or a basal setting while these are potentially changing at the same time you are testing to validate them. 
You did not ask about another important setting. Some people refer to it as your Insulin Sensitivity Factor (ISF). In Tandem’s pump profile settings this value is referred to as your Correction Factor (CF). It the amount your Blood Glucose (BG) is expected to decrease after bolusing 1 unit of insulin.
For example, if your BG is 180 mg/dl and eventually drops to 145 mg/dl after you bolus 1 unit, then your CF would be 35 (180-145).
If your CF setting is too low then your pump’s correction boluses will be too large and it will drive your BG too low. If the CF is too high then your corrections will be too small.
By the way, have you seen the following pinned forum posts?