General Head Boundary in Feflow

Hi,
I am a student writing a Master thesis using Feflow. In the User Manual I have found an information that I can describe known hydraulic head in a distance from the model boundary using Cauchy type BC.
I guess I need to put in the hydraulic head as fluid transfer BC  but I know that in/out transfer rate is also necessary. Is there any formula describing that material property in that case? I know one for the rivers but I think the one for general head should consider the distance between the boundary and known hydraulic head.
Thank you in advance for any advices
Best regards from Cracow, Poland

The transfer rate Phi is a resistance coefficient and can be approximated by Phi=k/d. k represents the k-value and d stands for the thickness (lengths) of the resistance “layer”. Usually, the transfer rate describes the resistance of a colmation layer located between the surface water body (e.g. river) and the aquifer. If you delineate the model domain far away from the river instead of along the trace of the river, d may represent the distance from the river to the aquifer.

If material data are available for this zone to parametrize your model it might be more accurate if you represent this zone in your model.

Thank you for your answer.
Yet I have another problem and I hope you can help me again.
How in FEFLOW can I describe dimensions of the river (Cauchy type)? I mean, I think it is necessary to define ex. width and depth of the river as ther area ot exchange can be found in the formula Q = A*phi*(href-h).
In my thesis I compare results of simulations from FEFLOW and MODFLOW models, and I can see that there are big differences in results when it comes to the rivers - I think that the problem is that in FEFLOW I haven't defined the dimensions of the river...

If you assign the Cauchy BC vertically throughout the layers, the cross-sectional area is automatically calculated by the lengths (along the trace of the river) multiplied with the saturated thickness.