I have a fixture that is failing due to inadequate contact surface of thread of bolts (5-16"-18)  between two flanges ( thread stripping and breaking). The bolts are torqued at 150 lbf-in each. The current fixture is using a 0.75 inch bolt. But when i replace that with 1.25 inch bolt in the actual fixture under the same pre-load of 150 lb-f, my fixture does not fail anymore as there is adequate thread  contact between the two surfaces and the bolts.

Now, I intend to replicate the same scenario of my physical model in Solidworks. I imported both the bolts ( .75 inch and 1.25 inch ) from my standard tool Toolbox as it gave me the flexibility to auto convert the toolbox fasteners into bolt connectors while defining the connectors later during simulation. I have defined the thread for 5-16"-18 in both my flanges too ( so as to maintain uniformity between between the thread and bolt )  I have been careful in defining the length of the imported bolts from the inbuilt Solidworks Toolbox library for 0.75 inch and 1.25 inch, respectively ( for both the bolt stud and thread length, as it is a fully threaded bolt in my actual situation). But my simulation results ( stress,displacements etc for the fixture and even bolt stresses ) are exactly the same for both the scenarios even though the bolt length have been defined differently in the model tree..

What should i do so that the difference of  impact for change in length from .75 inch to 1.25 inch is reflected on stresses and displacement on both the fixture and bolt ? Attached is a screenshot of my simulation module for static load analysis.

Thanks in advance!