I ran a Champion Radiator in my 52 F1 239 for years, never overheated, got hot but never went volcanic. That includes the Arizona summers. Chap
Cooling capacity does make a difference. Not to say reduced would not work.
Put two pots of water on the stove at the same heat and time. One is 1 cup of water, One is a 2 cups of water. Which to boil first.
Same if...If you put two 55 gal drums plumbed on the front of your car, you'd be highly unlikely to ever overheat. Maybe timing, block restrictions, over bore,...etc. Certainly a radiator that is restricted would not help.
No matter the temp sensor, even if they can be restrictive in summer or high heat ambient temps.
Naturally 1 cup will boil faster, but before long the second will boil also. Practically speaking, if a radiator has a little more water than another one, if the engine is producing too much heat, both will boil within a short time of each other.
Have you retimed the car since you put the Pertronix in? I installed one in a 350 SBC I had in a boat years ago and when I tried to start it, it backfired a couple of times, hydro-locked, and broke a rocker arm (one of those cheap aluminum rollers Speedway used to sell). I double checked everything over (thinking I had crossed a couple of plug wires) and everything was correct. The only thng I could think of was that the Pertronix somehow had an effect on the timing. I retarded the spark, and the engine started and ran pretty decent. After I put my timing light on it and moved the timing so the light was flashing on the pointer properly, the boat ran great and I never had another problem with it. I don't know exactly how those crazy electronical things work, but I definitely had to reset the timing after I installed the Pertronix. (And bought another rocker arm.)