As of LCOS 10.94, you can specify a common minimum MTU for all channels of a load balancer.
In LANconfig, you can find the new parameter under .

- Minimum MTU
-
This value can be used to specify the use of a common minimum MTU for all channels of a load balancer.
When using Dynamic Path Selection (DPS), it is recommended to set this parameter to
"Yes".
Important: If the MTU of the load balancer is explicitly overridden by an entry under , then all channels use exactly the MTU specified there—regardless of how the "minimum-MTU" switch is set and regardless of what may have been negotiated on the channels.Note: Under , the MTU of the load balancer is only displayed if it has been explicitly configured.