Instead it is part thickness distribution with respect to injection point (gate) towards the extreme point on the melt flow path i.e, last fill point. A good injection molding part thickness should always decrease (not uniform) along the flow path and that thickness decrease magnitude is the prime factor responsible for sink marks.
Basically injection (processing) pressure and temperature are primarily polymer and then mold and machine dependent. i.e., injection melt state variables., So part form / features have very less to do with setting injection melt state.However a good control to prevent sinks can be achieved by increasing packing intensification rate, this technique can considerably compensate thickness distribution variance also, which is quite often.
if you have ANY draft, the force will only be a peak force at the instant of the core break away. Typically if we had a 4 cavity mold- we put one cylinder on center. This would be for the larger size nozzle. If we made 8 cavities we'd go with 2 cylinders out board near the guide pins. I can't ever remember building any of these with larger than 2.5"- 3" dia. cylinders. You might find some of these products at builders supply stores that sell building adhesives and epoxies for setting anchor bolts in concrete.
I have seen hot runner internally flooded with plastic because injection parameters and settings are wrong. For example: mold cavity fill time too long, which causes the material to freeze up close to the injection points; then hold pressure applied onto frozen injection points—> the molten plastic has to go somewhere, maybe into your hot runner. A good symptom for this problem is if you have material leakage at the main mould entry valve gate and plastic creeping back up your screw cylinder - because the molten material cannot get into the frozen cavity.