No difference hard or soft here-just varies from tent to tent.
This is a shape question-not a hard/soft question. Check the height/width on whatever you're comparing. Still, if you're putting a tent on top of a roof rack on top of an SUV I'm not sure why you suddenly care about aerodynamics here.
I have no idea, just noting that there's really no difference I can tell (except marketing) between softshell/hardshell tents.
The ease of setup is a bit subjective, but no cover to deal with/store and just pop a few latches and your in business with a hardshell.
While I agree that aerodynamics isn't something that is a huge deal but...a 20" square up top will be more of a sail than a hardtop.
Just to correct a few things here since I have owned both types. There is a drastic difference between soft and hard shell tents.
ARB Simspon III
Loaded weight: 160 lbs
Setup time: 5-8 minutes
Take down: 10-15 minutes
MPG: 11-12
Pros:
-So much room for activities.
-Looks dope, expo as f***. "Totally overland brah" /mocking sarcasm
-Dry/concealed entrance.
-Doesn't take up whole roof rack.
Cons:
-Heavy noticeably more than hardshell even while driving.
-Setup/take down requires 4-5 trips around truck, straps, zippers, tucking.
-Packing up in cold weather, primarily zippers, sucks balls.
Magiolina Air Top:
Loaded weight: 130
Setup time: 40 seconds
Take down: 3 minutes
MPG: 14+ Aerodynamics. They matter.
Pros:
-40 second setup, no BS, release three clips, put up a ladder done and done.
-Comfy, cozy, better mattress, smells Italian.
-Lighter feel when driving.
-More MPG. 3 mpg stacks up on those 3,000 mile road trips.
Cons:
-Slightly less room than the ARB, but makes up with tons of storage pockets.
-Takes up entire roof rack, no room for firewood/chairs.
-"Rally" straps suck balls if I'm honest.
Now, I'm not 100% certain how the iKamper is going to stack up to the Airtops and James Barouds of the world, but they look nice. The ease of setup/take down of the hard tops vs soft shells really cannot be overstated. We have 50+ nights in both and the hard top has been the biggest game changer since going to a RTT in the first place. Literally next level.
Happy camping!