Ah, I may have answered my own question...although I'm too inexperienced to fully understand why yet. I changed my querystring from the above example to this simpler format. (Only showing car* names in this case.)
var queryText = '<QueryPacket xmlns="urn:Microsoft.Search.Query" Revision="1000">'
+ '<Query domain="QDomain">'
+ '<SupportedFormats>'
+ '<Format>urn:Microsoft.Search.Response.Document.Document</Format>'
+ '</SupportedFormats>'
+ '<Context>'
+ '<QueryText language="en-US" type="STRING">Carl* Scope:"People"</QueryText>'
+ '</Context>'
+ '</Query>'
+ '</QueryPacket>'