Thank you rahmanbar for sending a personal message alerting me to this thread. I am sorry to say I had overlooked it. I hope this answers your questions.
The hold is determined by sum of three factors, the length of stay, room rate and tax, and something called the incidental factor. The first two are simple math, you take your room rate and tax and multiple it by the number of nights you will be staying. However the incidental factor is less constant. This amount is based on the typical spending habits of the property’s guests. This means you can expect to have a much larger hold at a resort location than you would typically have at an Airport location because guest tended to spend a lot more on incidentals. Likewise guests typically spend more at certain international locations than at many domestic locations.
Once the incidental factor is created, like Socrates said, there is no human determination of what the hold amount will be. The hold is determined and processed by the hotels system based on the factors mentioned above.