Never could understand the purpose of clip-ons with an ocean-going fuel tank. (I know it's a personal preference) At my age, an hour ride is all I can do with the weight on my wrists. A smaller slimmer tank will hold all the fuel I need. Have you tried the low-rise, narrow European bars? I use them on my Interstate and with the rearsets make a nice comfortable ride you can still flick in the twisties. (Tho' a recent low-side reminded me that it's still '70's handling).
I am currently changing my 850 cafe racer from fastback tank/tail and PR fairing with clipons to full PR tank and seat with slightly higher clubman bars to allow me more seat time before I break. If I could get flat Vincent-style bars under the fairing, I would use them.
Sadly my 900SS Ducati bevel is so extreme with long reach over the tank and low placed clip-ons that it gets very few miles each year (owned it for 15 years and have put only 5000 miles on it). The more modern 900SS SP is much more ergonomic.
Most Interstate/clip on combinations I have seen have dimples in the side of the tank for clearance. Either intentional or accidental.