numeric models from drillholes information

Hello everyone
I am using 3 drillholes to compute a numeric model.  It's a very easy setting, 3 values only as numeric attribute for the layers. I expected a result similar to the image below (obviusly a less intricate model) . This image is the one given as exemple in the help seequent page 

The only result I can obtain is a numeric model with a strong horizontal distribution and almost non vertical variation. I don't really understand what the problem can be.
it can not be the amount of input information cause with a dataset of 6k drillholes the result has the same problem.
p.s. I know that the first image is  a 'neew indicator rbf interpolant' model and the second one is a 'rbf interpolant' model, the result has the same problem anyway

thank you to anyone who can provide some solutions