Thank you all for very helpful information and insight. There are certainly many variables, and different settings.
So with that in mind, I see that this group can likely help with my current design issue.
Currently, most everything on approach is set for a 3 or near degree GPA. The ILS, the obstacle surfaces, TCH and touchdown zone. In trajectory based management, I am finding that for many of the larger aircraft, that a 3 degree GPA causes energy management issues. I am also noting that with the advances in aerodynamics, and OPD, that the 3 degree GPA is a bit too steep, and a much flatter GPA, even down to 2.5, works much better.
Keeping to the 3 degree GPA, these differences are causing TOD issues, and energy management problems, such as speed flaps and other de-stabilizing measures, and excessive speeds on touchdown.
In efforts to optimize the trajectory, I am looking for a much better sweet spot on approach. I know that it will likely be a range of GPA's depending on the AC.
There is certainly no criteria to support this, so I am looking to the operators such as yourselves, for help, in realistic design, and perhaps new criteria. I am also looking for support on this issue, if this wont work for the aircraft and the operator, then please feel free to tell me I need to focus elsewhere, or have another beer.