Best practice for dumping Sybase database is as follows for compress backup… 

Dump DB

sp_dumpoptimize 'archive_space=maximum'
go
dump database ${DATABASE} to "compress::${DMPFILE1}" stripe on "compress::${DMPFILE2}"
go
sp_dumpoptimize 'archive_space=default'
go

Dump Tran

dump tran ${DATABASE} to "compress::${DMPFILE1}"
go

The reason for optimization being max is in case sybase mark a page as corrupt and de-allocate it will still be backed up so you can recover it from the backup.