The issue is the control of the installation vessel position and actual response of the tensioner active control system. Some issues that are significant is that the actual tension control is upstream on the vessel with considerable frictional resistance prior to leaving a stinger (inertia of pipe, inertia and friction of rollers and tracks).
The use of .15% unit strain was initially devised by Shell for their projects which entered into new depths and diameters without a corresponding increase in lay vessel capability. While buckling for most pipes will be above the 0.15% unit strain, the idea is to avoid the buckling.
Reducing the factor of safety could be done but I would think that a specific non-linear FEA of the pipeline buckling and residual curvature would have to be performed along with the vessel capabilities and the environmental sea-state that can surge the vessel and change the tension.
Vessel motions affect sag-bend and stinger tip strains more in shallow water than deep water. In deepwater, where thrusters are also in the tension control equation there could be a case for a reduced factor of safety…but not without a thorough analysis to meet the intent of 1111.
My 2 cents.