As long as you feel safe with it, it's up to you.
My heat or air from the furnace comes out of the floor, therefore low.
As far as it rising, well, all things being relative, it is still heavier (wrong, see below) than air.
That is why my FR manufacturer installed my CO detector low, about less than a foot off the floor, near the furnace.
OK now, I'm gonna correct myself. I did a search about this and there are myths about it, etc. CO is actually lighter than air as your numbers point out. And several comments are made about it being diffused etc. So, I'm just saying, they are usually installed low. But do what you're most comfortable with. Nice comments though!
I know of a few friends that have died from CO and either way, it is dangerous stuff......
I also found this:
Here is the recommendation at the end:
"My recommendation: buy a good plug-in detector! If you want, get one with a battery back up. Put it near any potential CO source and another near your bedroom(s)."
2012 Lacrosse, 308RES.
2013 Ford F150, XLT, 4x4, Supercrew, Eco-Boost.
Lee, Dawn and "CoCo", the dog!
2015 Overnight Camping Days = 25, States Below: