The white circle is used to locate the border of fisheye image. Its position is determined by both the fisheye parameter value and the levels (Brightness, contrast, saturation etc.) of the current image. So sometimes you find it uneasy to make the white circle surround the fisheye image properly by adjusting the fisheye parameter slider, if so, you may use the arrow keys (left, right arrow keys) in the keyboard to adjust the slider. Moreover, if the two fisheye images are different to each other in brightness and contrast apparently, please adjust image levels by rightclicking on the image with your mouse.
To see is to believe
Have the same equipment and the results ( matching) are very good AS LONG YOU SPEND SOME TIME on leveling your tripod. I do that by the use of a surface spirit level (home depot) using the FCon02 Rotator platform where you mount your camera ( prior to mounting the camera)
I asked the same question as maureen some months ago.
It seems to me that the parameter sliders is a bit of a hit and miss afair and it's unclear exactly what one is doing.
I do have ipix's 'builder' software, dare I say it, but I never use it for obvious reasons. However, 'builder' does offer much more control in its fisheye parameters, i.e. radius, tilt, X, Y and Z movement, etc.
I also use ipix's 'rotator head' which does make like life considerably easier when using Panoweaver, for the focal point of the lens remains exaclty on the axis of rotation.
Panoweaver is a great product, but its parameter control is its weakest element and I hope that the approapriate investment is made to improve this minor flaw.