With FileMaker Go I find it best to Set the zoom level at 100% and lock the ability to change, this stops the whole screen moving around. And you can have a script to set the lock off when you want the ability to pinch and zoom if part of your app.
Also set the layout size to not be bigger than the device's smallest screen size if you can, and use the anchors to expand the layout objects, this also help reduce scrolling.
Specifically with the Web Viewer you need to set the focus to this when you loading the record, so having a script run via a trigger should achieve this, see if running the script step Set Web Viewer [Object Name: “NAME”; Action Reload], or Go To Object [Object Name: “NAME”] works the way you want it to, it should bring the Web Viewer into focus ready for the user to scroll straight away.
I hope this helps