Interfaces trafic

Hy, i’m wondering why trafic on eth1 is different by eth2 traffic when queues are on. Usualy with 3 - 4 Mbps less than eth2 on Tx
Router is used as a firewall ( ETH1 bridged with ETH2 and ip firewall activated on bridge)
On eth1 trafic enters
On eth2 goes out

Hi, perhaps the output requests of the router makes this diference?