For a BJT model, the parameters Rb, Rbm and Irb determine the base spreading resistance. The resistance is Rb at low currents and falls to the value of Rbm as current increases past the value of Irb.
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The base spreading resistance is not present in LTspice unless it has been specified in the model. Many models use Rb=10 as a default value. There are many thousands of garbage models in existence which bear only a passing resemblance to the BJTs they are named after (likely the result of a failed attempt to batch process a dataset into SPICE models).
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Rb can be estimated by measuring the base voltage noise of a transistor at the collector current you plan to use it at. This does not always give the same value of Rb as the high frequency estimation method where you determine Rb based on the rise in transconductance as frequency approaches Ft (this is possible with s-parameters).
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There are still other methods of extracting Rb that are given in multiple long PDFs about the SGP model, although I can't find any of them at the moment.
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Here is a page with a calculator for using the noise method:
http://www.dicks-website.eu/low_noise_amp_part4/part4.html
