How vital is it to accurately know the construction details of the formation in terms of pump inlet placement?

It isn’t critical at all to know. If you did know something about the nature of the formation surrounding the bore, for example if you had interbedded layers of high and low hydraulic connectivity or specifically a fractured flow, try to place the pump inlet where that is.  But without any knowledge of the formation, anywhere you put the pump inlet you eventually get to stabilized conditions in the well and a flow rate of average concentration.