First try just deleting the old CHM before you compiling a new one.
Then try compiling to a different folder if that does not work.
Once a CHM has been opened I believe it remembers the users settings, in this case yours. If you put the CHM on a different machine, it would likely be OK the first time.
See www.grainge.org for RoboHelp and Authoring tips
Peter is spot on. Normally the CHM stores its screen coordinates in a hidden file that stores coordinates for all CHM files.
One way to see it adapt to your desires is to delete this file. But that also would affect every other CHM on your system. That may be undesirable. The other way is to simply use a variant on the CHM file name. Because it is a new file, it would then store the new coordinates.
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Thanks both to Peter & Rick for their suggestions. It was successful after I deleted the .chm file, made the changes I wanted, and then regerated. I do have a second help project that I keep on the same hard drive, but in different folders, and the other chm was not affected when I changed this one. Thanks so much!