The dynamics of laser-imploded pellets are studied to isolate those features which are essential to achieving high compression and large ⟨ρR⟩. Under the ideal conditions assumed here (e.g. no photon or electron preheat), the three-parameter hinged-ramp pulse (an appropriate sum of two linear ramps) is shown to reproduce the behaviour of optimal (i.e. singular) pulses and is used to investigate and control the hydrodynamics of the implosion.