My wheel alignment tech this time around probably did the best alignment job I've ever personally experienced. Thanks to this thread I was able to get a good starting point for a balanced compromise between performance and tire wear (basically evening out the numbers within spec and dialing in 0* toe in the front). But after doing some high speed canyon drives, straight line stability above 50 is lack luster... I'm constantly correcting to keep the car straight.
Before the alignment I installed the 0 offset RFC lower control arm bushings but perhaps I should have gone with the offset bushings for increased caster since I'm just at the edge of spec. Positive caster generally increases straight line stability at the cost of making the steering heavier.
My question is, which bushings should I get to increase caster given my current alignment below? I don't quite understand the +/-20 offsets as I Iook at the caster range of 8.0* to 9.5*.
Any other suggestions?

I found this info on the RCF bushings in another thread...
2016 RC-F
48075 - BRACKET SUB-ASSY, LWR ARM, NO,1 - Right
48075-24010 , OFFSET:0, REFER R/M
48075-24080 , OFFSET:+20, REFER R/M
48075-24090 , OFFSET:-20, REFER R/M

48076 - BRACKET SUB-ASSY, LWR ARM, NO.2 - Left
48076-24010 , OFFSET:0, REFER R/M
48076-24050 , OFFSET:+20, REFER R/M
48076-24060 , OFFSET:-20, REFER R/M

 

The +/-20 offsets will raise or lower the caster by about .3 degrees. Looking at the caster on the car now you should be
tracking to the right, car will tend to track towards the lower caster. You would want to put a +20 bushing on the right
side and raise the caster up to around 8.0, you could also put a -20 in the left and lower caster to around 7.9. That should
get the cross caster closer to 0 which is ideal.

You may also be able to get the cross caster closer to 0 without the need for offset bushings by doing a sub frame
adjustment, a knowledgeable alignment shop would be able to assist in this.

 

You can also try moving the rear bushing by loosening the bolts and prying it outward, then retightening the bolts. I just put Figs solid bushings in the rear on mine and the caster got better immediately, but the camber balance that used to be perfect is now 0.5 cross difference. That's usually a subframe adjustment, but clearly this difference is a result of dropping both the LCAs, servicing the polyurethane bushings in the front, and putting everything back together with the new solid bushings in the rear.

The rear bushing location is primary for caster, the front bushing location is primary for camber, but any change in either position impacts both camber and caster. It's just the nature of alignments. See the attachment here to understand the cross pollination effect - this is from the Supra service manual, a chassis with full adjustment capability.