As a crack tip approaches a free edge, its stress-intensity factor rapidly increases and tends to become infinite.  One can look at the width contribution as a separate (multiplicative) b factor in the same way that the width contribution affects the solution of the center-crack remotely loaded geometry.

Recall that the stress-intensity factor for a loaded panel of finite width W is given by (see Table 11.3.8)

which leads one to conclude that the (multiplicative) width effect b factor required to convert the infinite plate solution to the finite width solution is

Other width correction formulations yield similar results.  Most SIF solutions have the width correction included in the formulation if it is necessary.  If one is aware of the need the formulation should be checked before using it in an analysis.