Webgate users have issue with Cisco Telepresence

If user login using Cisco Anyconnect (VPN), then video conference through Cisco telpresence is good. but if the user login through F5 webgate using RSA token then in the cisco telepresence , the screen is black out. We change the MTU value from 1500 to 1190 and its started working.

But now user dont want it to change the cisco telepresense settings rather than something needs to be changed in the F5 tunnel so that all webgate users can access the telepresence without manually changing the settings .