For me in 1080i 4x3 mode, 4x3 content is full screen and 16x9 content is pillar boxed in fit to screen mode and both are full screen in full screen mode.
That sounds to be exactly what I want. Maybe I have something setup differently somewhere else.
Here is how it is currently configured:
1. PCH: 1080i 60Hz, Fit to Screen, 4:3
2. Startmeup: just "/etc/mvpmc/mvpmcx2 &", no extra settings
3. config.xml (modified to over come overscan issues)
<MVPSendIncrementalUpdates>true</MVPSendIncrementalUpdates>
<MVPClientType>PCH2</MVPClientType>
<MVPWidth>1184</MVPWidth>
<MVPHeight>672</MVPHeight>
<MVPOffsetX>48</MVPOffsetX>
<MVPOffsetY>24</MVPOffsetY>
4. PCH is connected with composite cables
After playing around a bit more I'm starting to think that it might be the TV itself doing it. It has a "16x9" enhanced mode where it compresses things it thinks are vertically stretched 16:9 to 4:3 back to 16:9. Unfortunately it is either ON or Auto. There is no OFF.
Thanks for your help. Sorry for the confusion in the other thread!