I have my Cal King and Mex Black King in a rack setup on top of 2 sand boas. In the same room I also have another sand boa and my BP. My new corn is currently in quarantine in another room, but will be moved in the same room. As long as you quarantine your new snake, observe for signs of illness, etc before moving below your BP I don't see a problem. I have my snakes checked by a vet before moving them out of quarantine into my herp room. Also, be sure to have really secure lids on your tanks....just in case your Cal King does decide it wants to visit it's upstairs neighbor. 

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1.0 Ball Python "Aragorn"
1.0 Kenyan Sand Boa "Gimli"
1.0 Saharan Sand Boa "Frodo"
0.1 Rough-Scale Sand Boa "Arwen"
0.1 California Kingsnake "Gentoo"
1.0 Mexican Black Kingsnake "Indigo"
1.0 Snow Corn snake "Chile"
0.1 Australian Cattle Dog/Pointer
"Kira"