tribo - someone might have the technical numbers but 'buckets' divert 100% of the air.
With fan engines only the fan(N1) airflow gets diverted. The core thrust is not part of the reverser thrust system.
Accelerating a fan(high bypass) engine in reverse actually increases the forward thrust from the core but it is offset by the increased stopping power of the fan(N1) thrust being diverted.
And different engines have different effectiveness. The PW engines on the 757 have better reverse thrust than the RR powered 757's.