I used 50 ft of copper tubing wrapped around a corny keg to make my IC.
I typically brew 10 gallon batches in a 20 gallon SS kettle.
The top of my coil tends to stick above the wort (no big deal) by an inch or so.
Regardless, it still chills 10+ gallons in under 15 minutes to ambient temps.
If I had wanted more of my copper tubing immersed in the wort, I could have used a cylinder with a larger diameter (e.g., a 5 gallon Homer bucket). However, when I was contemplating my design options, I was thinking that, long-term, I might like to use this IC as my "pre-chiller" and be able to place it inside a bucket or cooler of ice water--hence the tighter coil.
I made a handle out of PVC pipe, wooden dowel fillers, and black electrical tape to avoid burns. It makes manipulating the IC (i.e., whirlpooling) and lifting it out effortless and safe.
No regrets.