Continually updating parameter used for EKF in simulink

I am developing a simulation of my project using simulink, where I have a physical representation of my system. From this physical model I get several parameters that I use as inputs into an Extended Kalman FIlter(EKF) block which estimates a desired parameter.

The measurement covariance(R) of the EKF is a product of one of the parameters from my physical model. What I need is for R to be updated at each step during simulation, so the EKF configuration effectively changes at each step as well.

I have tried creating a variable in the base workspace called R, and placed a matlab function before the EKF block which updates the variable R with the new parameter from the physical model, using assignin() function. I was hoping that this means that the EKF will have a new R each iteration but it is not the case. R does not update. I was wondering if any one had any idea of how to do this?

Many thanks, the help is much appreciated!

Kind Regards,

Jeremy