Unless flow is grossly turbulent, flow through a restriction with a given characteristic media is proportional to pressure delta across that restriction. This works with head ports, exhaust, oil pumps, and everything else including your throttle body.
If the throttle body is flowing enough for NA on that engine and you increase boost, the flow will go right up with boost. If you go from a N/A pressure drop of 14.7 psi between atmosphere and perfect vacuum to 20 psi boost with no port or throttle body or temperature changes the air flow increases (14.7+20)/14.7 = 2.36 times. You get 2.36 times the base power minus the pumping power required to run the compressor.
The bottom line to this is if a throttle body is good enough at NA for your base power without being a choke point, it is also good enough for the boost. The throttle body only needs to be larger if it is a choke point or restriction without boost in the same combo.
This is the same reason a high volume pump can't "pump the pan dry" unless the high volume pump adds a tremendous amount of additional oil pressure. Flow is always proportional to pressure differential across the restricted path.
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89 LX. 363, single turbo, Super Vic EFI, TFS high port heads by TEA, solid roller, glide. Holley HP EFI. (exact combo varies)