These constants don't cover all the possible options.
There are two constants:
These relate to using OFB mode in 8-bit feedback mode and using the same feedback length as the key
There is one constant
MCRYPT_MODE_CFB which uses 8-bit feedback mode
There ought to be a constant
MCRYPT_MODE_NCFB which uses the same feedback length as the key.
In fact you can just use the option 'ncfb' in mycrypt