Does FortiClient have any ability to alter packet size?

I've set my SSL-VPN firewall policy tcp-mss-sender and receiver to 1350 and it's cut errors down substantially (yes, horrible data lines). But one user needs it set even lower. 

I can reduce the whole firewall policy even more, but I was wondering if FortiClient has any ability to affect the packet/message size -- Note: I'm not talking about change the mtu on the device, I only want to change my VPN communication.

Thanks.