I've never heard anything like what you posted. That is just not how insurance works. There is no % of value that you just automatically lose in an insurance claim. You also don't just lose out on anything and everything on board. Know what type of policy and coverages you have and what items are covered under what policies.
When I quoted my insurance, a PIU was considered a base explorer by many insurance companies. There are many factors that can affect a claim - condition and mileage are two big ones. If your insurance company/coverage is not good, best suggestion is to find one that is better or, if you have a claim, involve an attorney to help you negotiate the best possible outcome (YMMV if cost is worth it for you).
It sounds like you may want to move, or at least park your vehicle in an enclosed garage or fenced area if break in is a bigger deal than outright theft of the entire vehicle.
The number / percentage came from my experience of totaled claim of my family members. The way I got it the number is how much they paid us vs how much to get an same vehicle from the market with similar criteria (like mileage, options). For example, one of the totaled vehicle was a toyota SUV, which was new, under 5000 mileage, no prior damage. The check they send us for sure didn't make close to the market price not even close to if I'm getting it from a used market, not to mention getting a new one. The loan insurance covered the gap so we cleared out from the loan, but still losing what we have already paid for months. Consider if you have no GAP insurance, you have to pay the make up yourself, which results in the auto lost I mentioned. Even if you are not in a loan, you still lost the make up portion (but the good side is you don't owe anyone).
They did treat PIU as explorer, but they treated it like a base explorer without any option and consider not so good condition (that's what I heard from my insurance agent). Which means with the high mileage already on the car, they aren't going to pay much for replacement cost.
Also, as least for my insurance (which is farmers), they repeatedly told us they will not cover anything that is not permanently mounted to the vehicle (like any accessories, valuable, etc.). They said those coverage should be under rental / home owner insurance which cover property lost, but not auto policy (which I mainly addressing to). Maybe different company has different policy, but this is base on my experience.
Last but not least, simply too hard to relocated as I'm getting a bargain for my current rent, which make it still affordable replacing some broken glasses. Unfortunately there is no alternative parking choice here (there is no enclosed parking within couple miles except those doesn't open to public). The parking lot I'm using now used to be a enclosed private parking, but the new landlord just decided he wants some extra cash and opened the door to everyone, without any security measure, and have a big sign on the wall saying he is not responsible for any lost and broke in.
But after putting all the time and effort into setting the vehicle up how I like it, be a shame for it to get stolen by anyone with easy access to Ford fleet keys. That and I doubt insurance would cover true replacement costs.
