Placing a marker, hand mat, or anything else that close to the hurdle is either going to take away running power or is an indication of weak run training needing more attention. These props are set out to allow a last second adjustment during the last 2-4 strides, and adjusting means altering stride length away from the bodies own ideal pattern. That means shortening or lengthening to compensate for.......1-2 feet of running error?.....in a 70 ish foot run?
If you want an example of the ideal, I'll offer up world class sprinters, not for their speed but for their stride consistency.
The number of strides taken in a 100 meter dash is the same for each runner....every time, over and over and over. Even more interesting is that these runners have fairly similar bodies, and a majority of these athletes take 41 strides. So there must be a correlation between running fast and being consistent. BTW that Bolt guy from Jamaica.....he takes only 40 strides.
I haven't lost enough of my sanity over the sport of gymnastics to sit down and mark out where the last foot lands before these sprinters hit the finish line, but I can imagine for each athlete there's a consistent zone about 2-3 feet long where stride #40 begins, and it's always on the same foot.
Maybe I'm making too much of this, but I just can't see the need to adjust stride length to the extent that you need a "target" on the runway. These sprinters run 330 feet and have a deviation of about 18 inches long to 18 inches short (yeah it's a guess, but it's probably a good one). In vault parlance that would be the equivalent of 4 inches plus or minus on a vault run. Just say'n......
Getting that consistency is pretty easily done by starting young vaulters with a 3 or 4 step run to a punch off a springboard rebounding onto a resi-mat, stacked mats, or the vault. When they've "mastered that run they can add 2 steps and do a modified handspring onto a stack or the vault. The next two steps puts them at 6-7 steps, and when done with maximum effort that's enough for handspring vaults for kids that have any business doing a handspring vault in the first place. So if they can't run the entire length of the runway with speed and confidence, give them a shorter run and an easier vault to work on until they can commit to a full speed (for the steps allowed) consistent run. That's the easy way, and that's what the sport is all about...doing things the easy way because it's not all that complicated in the first place.