I can tell you everything you want to know, if you give me enough information.
The fact that it is private property doesn't mean anything one way or another. Ordering a police report after the fact will help you zero. Conversely, it doesn't matter if the other person files a report after the fact either, so it doesn't matter what they say.

Go here: http://www.accidentsketch.com/ and work up an accident diagram and explain what happened and I'll tell you what is going on.

Without any information at all, I can tell you that accidents where both parties are backing are usually broken up into 50/50, and no one gets anything from the other guy (in Colorado anyway). So if you are getting anything from Allstate, then you must have been told that you are less than 49% at fault.

If you don't feel like putting your business up here, send me a PM and I can give you more information.