[BM 1.11][SEV 1.58] The 300 (militia troops, that is)

In my current solo game, I've heavily bombarded and then invaded a neutral AI's planet. No atmosphere (domed), 7 M population, 4 badly damaged fighters, no WPs or troops, and 3 research research facilities with varying levels of damage.

Invaded with 150 troops dropped from a medium freighter.

When ground combat came up during turn processing, I wound up facing 4 badly damaged fighters and 300 militia troops! The sheer number of units on the screen dropped my system performance down to about a frame every 3 seconds. User interface controls were so sluggish as to be unresponsive.

To add insult to injury, every single enemy unit turned tail and ran (at a snail's pace) from my massed troop formation. They had weapons, and supplies (except for the fighters, that is), and should have engaged my units. But nope, they scattered, and I wound up destroying or damaging maybe 25-30 units by the end of combat, which took a darned long time to complete.

I was planning to invade the AI homeworld (with a lot more troops)since they breathe a different atmosphere than my race, and I can use that, but the number of troops that will be on screen would make any such invasion an all-night affair.

I recall seeing a different thread about the same topic, but thought the issue had been resolved. Is there something in the settings.txt file that I missed? Something I can tweak? Something?