AIMinPassesPerTick=3 // minimum passes per tick (can use more accurate spring/damper/torque values, but takes more CPU)
This value in the .hdv file is important because it means how often the AI gets updated on the track, not only more accurate physics but they also seems to recognize the player more, so you can remove that idiotic drone feeling they have toward the player. I raised to 10 and it's better now. You can try higher values if you want. It doesn't seems to be CPU heavy. Please note: it will cause miss matches. Use it for offline only.
AI Brake_Power Usage="0.99000" // Fraction of theoretical brake power that AI attempt to use (can be overrode in HDV)
Also reduce this value in .plr and eventually in .hdv. This will prevent AI to bump your back while on heavy breaking before the hairpin. Reduce it to 0.95000 they won't go much slower really, they'll just brake as they should when they are not attempting a pass.
AI Mistakes="0.00000" // a range of (intentional) AI mistakes from 0.0 (none) to 1.0 (sometimes). Anything above 1.0 multiplies the frequency
Then raise this value to 0.2 at least. If you keep it at 0.0 AI will never miss a corner or a brake zone.
After these tweaks you can experiment with AI agreession value and see what works best for you. I'm using 15 % now. Hope it helps.
