I've checked all interfaces that I believe are relevant. There are some differences.
Interfaces on EX9200 connected to the SRX1500:
> show interfaces ge-4/3/0 | match mtu
Link-level type: Ethernet, MTU: 1514
Protocol eth-switch, MTU: 1514
> show interfaces ge-5/3/0 | match mtu
Link-level type: Ethernet, MTU: 1514
Protocol eth-switch, MTU: 1514
Interfaces on the EX4200 connected to the SRX1500:
> show interfaces xe-0/1/0 | match mtu
Link-level type: Ethernet, MTU: 1514
> show interfaces xe-1/1/0 | match mtu
Link-level type: Ethernet, MTU: 1514
Interfaces on SRX1500 connected to the EX9200:
> show interfaces ge-0/0/12 | match mtu
Link-level type: Ethernet, MTU: 1518
> show interfaces ge-7/0/12 | match mtu
Link-level type: Ethernet, MTU: 1518
> show interfaces reth4 | match mtu
Link-level type: Ethernet, MTU: 1518
> show interfaces reth4.62 | match mtu
Protocol inet, MTU: 1500
Interfaces on the SRX1500 connected to the EX4200:
> show interfaces xe-0/0/16 | match mtu
Link-level type: Ethernet, MTU: 1518
> show interfaces xe-7/0/16 | match mtu
Link-level type: Ethernet, MTU: 1518
> show interfaces reth0 | match mtu
Link-level type: Ethernet, MTU: 1518
> show interfaces reth0.515 | match mtu
Protocol inet, MTU: 1500