Fighters definitely cannot defend in a SBR. But, I think SBRs are overrated and should be avoided vs. any IC that is defended by AA guns. Think about it: your bomber will average 3 IPCs per turn, so after 5 rounds you have done 15 IPCs damage. By then, the odds are that you will lose at least one bomber - worth 15 IPCs. At best, it’s a saw-off. Plus, you run the risk of losing 2 or more bombers with bad luck.
I have found it much more effective to use the bombers to strengthen a regular attack, when they are well protected behind the fodder of cheap INF and ARM.