I noticed that Heavy Gun regiments never get to 100% TOE. They have enough guns but they seem to always max out at 69% TOE because of lacking support. Is this a bug or what would explain this?
Support squads above 100% need are not added to units. This is one of the very rare for the Soviet side units that has more support squads proscribed by TOE than needed by other elements. For Axis side this is common (and no doubt this rule exists for the Axis, to conserve manpower). In 1.08 support squads won't affect TOE%.