I have been working on a few form projects lately and am having an issue with setting default anchors in forms. Basically, I can't. I have tried setting them at FormPanel, Container and Fieldset levels, both using the defaultAnchor and defaults attributes (Done in Ext Designer).
I'll take a look at your project file and get back to you. In the meantime, do you know if your form fields still have their explicit "anchor" property set? Form fields will get an anchor of "100%" by default in the Designer, and I do believe they will override defaultAnchor setting.