User questions on Slide theory are addressed in this article:

In slope stability calculations does Slide consider the influence (in terms of weight) of the upper portion of a model if the limits for the slope are located lower?
No, and this is because of the limitequilibrium algorithm in general. The algorithm in Slide uses the method of slices. The failure surface is divided into a number of these slices. The forces on each slice are only due to external forces on that particular slice and the weight of the slice. There are also interslice forces due to adjoining slices. So, since the yellow material is outside the extents of the failure surface, its weight is not applied in any way to the force system of any surface between the search limits. The analysis is not like a finiteelement analysis in which loads have some influence in all directions. If you want something like this, RS2 is the program to use.
Yellow material does not affect limitequilibrium factor of safety

How does Slide deal with interslice forces in models with anisotropic materials?
Basically, the interslice forces are computed based on the assumptions defined by the method. For example, Spencer's method assumes a constant interslice force angle, Janbu and Bishops methods assume no interslice shear stress.
Table 6.2 in Duncan and Wright's book lists the various interslice force assumptions:
Duncan, J.M. and Wright, S.G. (2005). Soil Strength and Slope Stability, John Wiley and Sons Inc.