I noticed the Colonizer subsystem's potency (how many buildings it generates when establishing a colony) is, of course, whole-number integers, and incorporating and attempting to resize the module generates an interesting nuance; the mass, size and resources scale in .25-size increments, of course, until you go below the minimal amount for one building, at which point it minimizes the resource cost, size and mass of the module to the absolute minimum needed to enable it to produce one building (so it will bottom out, often in-between .25-size steps).
This, I found, provides an opportunity to really tweak Colony ships for maximum colonizing-bang for the resource-cost-and-size buck: instead of incorporating a single Colonizer module to produce X number of buildings on a new world (default/standard 3), I make my Colony ships with 3 0.25-sized Colonizers which gives 3 buildings for an absolute minimum of size on the Colony ship, minimized mass and minimized cost. It can give quirky non-.25-increment size costs (a mid-tech Colony ship I am now designing, for instance, has 15.89 of the 16 slots on a Light hull being consumed thanks to this quirk ... is there a way to resize other components more precisely than 0.25 increments?). I can use this to absolutely minimize the cost of a colony ship.
This tweaked colony ship I am making now, for instance, will build the standard 3 buildings on a new colony, but thanks to using the Colonizer size quirk and External Supports for the engine and Life Support modules (two full 4-size plus one 1.75-size), I am able to scale the ship down to 4.286-scale, quite cheap.