FWIW, throughout the day, underhood air will be more consistent than outside air! I know a good racer who had a beautiful '68 Cuda big block tribute car. He blocked the scoop with plexiglass because it was more consistent that way.
I have another friend who had a '65 Satellite with a '65 style scoop that ran off from time to time. The problem was turbulence within the scoop. He opened up a couple of small vents in the foam and the problem went away.
It helps if you figure out the optimum jetting for what scoop/no scoop set-up you will run. There was at least 1, maybe 2 jet numbers difference in optimum jetting between running with a K&N Stub Stack and without on my bracket Challenger. The Stub Stack was leaning out the A/F ratio by that much! Fresh air or without, and scoop configuration can also have an affect on jetting......then you have weather/seasonal changes!
I had a heads-up run in my IHRA Dart Sport at one race. Running a 14"x3" K&N air filter, I figured I'd pick up by removing the filter and just leaving the base to smooth airflow. With the changes I made and removing a little extra weight, I should have picked up a noticeable amount, but I didn't! Even with a good filter, my jetting was optimized with the filter and I leaned out a bit without it. I would have been faster leaving the filter on. Luckily I still won.