Condensate from any level could be collected and reused as boiler feed water, as long is its quality meets the boiler feed water specs.
 
In this case, the available lower head pressure of the condensate may not be enough to get into the existing return pipe line or into the condensate pot and hence would start accumulating at the source itself.
 
By modifying the return pipeline and lowering the receiver pressure, the condensate from below 4.8M level condensate sources also could be collected and pumped back to use as boiler feed water.