I'd keep as much out of the ground as well. Started with PAP, hand wrapped and installed in tile. Ripped it out the following summer after watching thawed ground in February. Too deep and into the groundwater that time.
The next run was Uponor (spelling may be incorrect). Guess what? I put this 18-24" down, way out of the groundwater. Still have heat escaping although not nearly as much but it's the first place to have green grass.
I have about 50' of exposed BI pipe in my garage. Only a couple times this past winter did I start a coal stove to warm it. The residual heat from the AA and the pipes maintain about 40°F all winter.
Just my $.02 of course.