The so called 10% rule is a guideline for applying resisted and assisted training as a means to making the athlete faster for their chosen sport. Here is the 10% rule as I have taught it and applied it over the years. In adding resistance it is best to not exceed a weight that that is greater than 10% of the athletes bodyweight or that will result in a time that is 10% slower than their best time for the distance run. In assistance, towing or downhill, I never want the athlete be be towed faster than 10% of their best time for that distance. Pretty simple, now you can call it a rule, but it is just a guideline.
Now you have to coach. You need to clearly understand the dynamics of the start, early acceleration, transition to top speed and top speed. Get them in an optimum starting position based on their strength and explosive qualities, their body dimensions- leg length, torso length and arm length and make sure that fits with the sport. Obviously, aside from track you do not have a block to push against so that will impact your angles and weight distribution. Once that is established remember the goal of the start is to overcome inertia by taking advantage of the “stumble reflex” you displace forward and get the first step down to create a positive shin angle to facilitate triple extension “extension reflex”. Then you are off to the races. The first contact is the longest time on the ground and as each succeeding step gets longer the ground contact time get shorter as you transition from pushing to running over the ground. You do not try to stay low, rather you let you hips run under you until you are virtually upright. As far a cuing, for me it is initially a push/push/push/push/action (Four to six steps depending on the distance and the athlete) gradually transitioning to running over the ground- striking (not pawing).
So this begs the question why heavy sled pulls or pushes? If you consider what I said above then they really have no place in a program to get an athlete faster. If you are training for a truck pull or your an offensive lineman that has to drive someone for three yards then use it. If you want to make someone faster at sprinting, don’t use it. Someone asked me about using heavy sled pulls to elicit a PAP response before sprinting. A better way is to do a standing long jump or a standing long jump onto one leg and sprint out, or bound into a sprint. A contrast harness (Bullet Belt) will also do the trick. Use movements that are dynamic and are closer in the range of motion and speed of movement to the desired end result. In my 45 years around training, a great many of those as a track & field coach, I know of no elite sprint or hurdle coach that has used heavy sled pulls. In my world that speaks volumes. Take that training time and work on mechanics, coach em to be better not tired.