Hi FTL
Maybe I didn't explain myself properly. I still don't understand fully all the nuances of the various race conditions, so this is secondary to 'best of the last 3
comparable'
for me.
Speaking only for myself, I find that if I can find the best 6f line, say, in a 6f race - not 5.5, nor 6.5,...and dirt to dirt, not poly to dirt or dirt to poly, I have more hits.
It was by sticking to this in Woodbine's 12th race Dec. 6 that I realized I had put in the last line the first time around, which was a 6.5f line. When I went back over it and changed it to line 4, the second 6f line, it put #8 squarely on top of BL BL for a $24.30 win.
When there are races where I can find lines this way for all the horses, then I look at race conditions and how each horse fits within those conditions. Is it going up or down in class,..a little, or a lot,.. coming back after a layoff etc. before I hide down to 5 the way I described above.
When that doesn't happen, which is, as you know, a goodly portion of the time, and I find myself with a race consisting of sprinters, routers, shippers, only turf, only poly all running today on dirt, I use the best of the last three... period. I then pay more attention to today's class conditions as compared to what the horses have faced in the past.
I treat 7f a little differently. I will use 7f lines in both sprints and routes if nothing else comparable is available. I like 7 furlong races. They make me happy.
None of the above includes Woodbine. Woodbine is Woodbine and I fear to use any other lines there. But I don't hesitate to use Woodbine lines at other tracks.

I hope that explains my thinking a bit more.
Barb