It' just a sim, and though it is a really great sim in my opinion, my actual launch data is never dead on with what OR predicts, so I don't sweat the small stuff. Doing that can stall a build or discourage a design from ever reaching fruition, where as I prefer my design/build stalls to be my fault or the fault of extenuating circumstances beyond my control.
If your talking about for HPR, then I can understand the desire to nail down every last thing, do to the cost and resources involved and lack of actual availability of airspace to fly in, but for anything else I would let something like that slide and base my design judgements on what is known about the general characteristics of the different common profiles of nose cones.
My actual launch data which I generally get from watching the video afterwards as I have yet to employ avionics save for an 808 camera, typically at best match OR's sim data to within 7%, and more generally fall into the 10-15% range.
Sometimes OR is off by a long way, but as long as I have a SAFE launch, it is still all good, and things are learned.
Oh, and welcome to the forum!!