I agree, I just had to deal with this on abi-0, except in my case I had to use unit 10.
If it can't be automatically detected, it would be nice if the installer had a cycle gadget to list the available units. Device names would be better. Unit numbers give you no clue to it's location.
I guess this is not a pressing issue. It's a pita and would really be tough for a newbie to handle.