Water Rocket Computer Model Problems

Here is the eighth Water Rocket Computer Model Problem.

This is a fairly normal water rocket running at 100 psi.

I have included the file details so that you can reproduce it yourself to investigate the peculiar nature of the maximum displayed in the screen shot on the right.

It is a plot of Distance Downrange as the output variable with Mass of Water (10g to 1500g) on the Y axis and Nozzle Diameter (2.0mm to 9.0mm) on the X axis with a post-thrust integration interval of 10ms.

The graph shows a long maximum that runs along the edge of the viable range.
At the cursor, the nozzle diameter is 4.33mm and this produces a downrange distance of 92m whereas at the right hand side (with the same weight of water - 606g), the downrange distance is only a tenth of this. What is the explanation?

 Variables Water Rocket Computer Model Problem 08 Rocket Mass of Rocket Empty 120 g Capacity of Pressure Vessel 2050 cm3 Rocket Diameter 9.5 cm Rocket Coeff of Drag 0.56 Nozzle Diameter 10 mm Constant K for nozzle 0.16 [ ] Launch Tube in use Not Used Duration of air impulse 50 ms [ ] Parachute in use Not Used Launch Tube Length 20 cm External Diameter 75 mm [X] Hollow Launch Tube Used Wall Thickness 2 mm Length of Tube Empty 25 cm Distance of Vent from End 0 cm [X] T-Nozzle in use Used T-Nozzle Diameter 4.75 mm Parachute Diameter opened out flat 1.2 m Parachute Coeff of Drag 0.9 Deploy () Apogee.( ) Timer 4 s Delay in opening 5 m Initial Mass of Water 850 g Pressure in Vessel 100 psi Height 1.5 feet Angle of Elevation 88 ° Speed at Angle of Elevation 0 m/s Temperature 10 C Environmental Gamma of Gas in Rocket 1.402 Density of Gas in Rocket 1.293 kg/m3 Density of Liquid in Rocket 998 kg/m3 Acceleration due to Gravity 9.81 m/s2 Atmospheric Pressure 1013 mBar Density of Air at STP 1.293 kg/m3

 The problem here is . . . 1. to find an explanation for the maximum being positioned so closely to the edge of the viable range.

The variables are in the table on the left...

If you give up or you think you know what is going on, look at the answers.