I honestly think the cap is fine. Put a mercenary space dock on control group 0, and tell it to not build if your total resources are below, say, 1,000,000 (in the ctrls-by-control-group menu). That way, you have 500k/500k at all times to refleet elsewhere. Make sure you've got, say, mercenary fighters on loop and rallied. That way, you will actually have a fairly big fleet sitting at home just waiting for you. Mark IV fleet, too. Always nice to get those little reinforcements.