Exactly, the higher the value already is, the less likely an increase will become. Here is an example of some smithed up equipment:
The crown, bracers and gauntlets got almost equal increases in DV and PV, while the armor got almost no PV increase (+4) with respect to the DV increase (+37)
Attachment 2574
gremlin - karmic lizard, dark orc, acid vortex, staring eye - dragon turtle, fairy dragon, ogre lord, minotaur emperor - pit viper, orc butcher - greater mimic, dark elven wizard, carrion crawler, dwarven child - imp - ochre jelly, dark elven archer, king cobra, goodwife - kobold shaman, magebane eye, floating eye, quickling king - giant centipede, hill orc sergeant, mimic hivemind, greater claw bug, brown bear, large gnoll - giant bee queen, giant ant warrior, shadow centipede, kobold