Nanoprobes are known to be high precision systems, which require preliminary modeling for thorough analysis of optimal working modes. One of most crucial characteristics of the special class of such beam lines is the so-called load curves (or surfaces). This paper investigates one of the types of intrinsic effects, i.e. fringe fields and their influence on load curves and surfaces, which make it possible to construct the purposeful search of optimal working regimes for nanoprobes. A number of different models for fringe field presentation are discussed in the paper. Analytical and numerical methods and tools are used for analysis and selection of optimal parameters for fringe field models.