A straight axle hangs down quite a bit more than IFS, not only just the axle. In spring under set up you have the springs, U-bolts and U-bolt plates hanging down, not just the diff (other than bashing the front diff into the ring gear).
IFS

SAS

Even thou there are more things to snag on with a spring under set up, the strength of a solid axle compared to IFS out weights the loss of clearance.
Bigger tires are definitely the best way to gain clearance, but if you cant go to a bigger tire or choose not to. You can shave the diffs, SPOA, high pinion 3rds, or switch to a custom high clearance axle.
Amilla