Here's my take on it:
If you only play an 8-2 exacta, and the 2 does not win the first post, it is IMPOSSIBLE to catch an 8-2 exacta on that game, if 8 runs it out, because once 8 scores the first point, they then face post 2, beat the, keeping the 2 scoreless. Same thing if you only play 8-1 and 1 loses first point. BETTER BET: 8/12, eliminating getting crushed on first point.
Also, generally, speaking, the trifecta results show how much more common 8/12/456 is, over 8/5/1234. It's just tougher to get a higher number to place if 8 runs it out, because that means all the lower posts must have no more than 2 points, and preferably one point. Like when you catch an 8-5-4. Often, post 1 or 2 win the 1st point, then 3 gets a point, then 4, then 5 runs it to post 8, and 8 runs it out. I've often hit very good paying 8-5-1's or 8-5-2's, because most people play the more common 8-1-5 or 8-2-5.