Yes, it matters. I mean, wireless paths, technically, can do 9k MTU for layer 2 if the vendor supports, like some units from Ubiquiti.
But the point is, layer 2 MTU should always be MAXED out on ALL Devices, even if it's different between them. Layer 3 MTU needs to be designed in a way that it ensures:
1. PMTUD works correctly in ALL paths and directions (MPLS TE? LDP? OSPF? BGP? GRE? WireGuard? Bridge, VLAN, VPLS? Etc)
2. L3 MTU should be 9k in the backbone on the physical ports, but you cap it wherever required on the layer 3 sub interface, such as LACP bonding to your upstream devices or the L3 VLAN interface towards another device etc
MTU design and training, is often something I don't see very often in network training programmes and certs. MTU itself is a piece of cake, however, when your network has all types of devices with varying MTUs, proper planning is required. Don't justify to yourself with this "1600" cap, do 9k MTU on the PHYs everywhere when possible to ensure future overhead room for anything.
My loopbacks are all 9k L3 MTU, most of my paths are 9k L3 MTU back-to-back, but some paths are 1500, some paths like wireless are 1500 on layer 3, but 1600 on layer 2 on the radios, but 9k L2 and L3 MTU on the transport ports on my PE router and P for example. Nothing breaks, because layer 3 MTU matches correctly between each termination L3, so PMTUD does it's job. No packet fragmentation or VPLS Control word bullshit nor frame drops nor MTU mismatch.
You can follow the MTU section in this guide:
viewtopic.php?t=176358
And this:
https://stubarea51.net/2021/07/20/wisp- ... -vpls-mtu/
