Without seeing your data, it's hard to give specific recommendations. However, cokriging and regression kriging work in completely different ways, so you shouldn't expect their results to align perfectly. I don't know if the difference is big enough to be worried about, but you shouldn't expect the maximums to be the same.
About the log transformation, again, it's hard to recommend whether or not to transform without seeing the data. But if you think a log transformation is needed, this is how you would proceed:
- Take the log of the dependent variable at the very beginning.
- Run OLS on the transformed variable, interpolate the explanatory variables and the residuals, and plug the results into the equation as before.
- This will give you predictions for the log of the data value. You would then take the anti-log (e^predictions if you used natural log) to get predictions on the original scale.
