From your description it sounds like you're not setting.
Basically this means that as you take off for your salto, you're dropping your shoulders and/or throwing your arms up and forward way to early. This results in the salto being very low to the ground, as proper technique is to "Set up" and then, after being fully airborne and upright, initiating your rotation (throwing the arms etc.)
There are ALOT of good drills for helping with this, in fact I just had to create a thread of my own to ask for ideas on how to fix this. However a basic drill that might help....
You'll need a minitramp or a tumbletrack. At the end, stack up resi/crash mats till its about your shoulder or chest height (if you're using a tumbletrack, head height if you're doing this drill off of a mini), then from a run, do a punch and do a front pike to your bottom (You'll land on top of the mats, take off from the minitramp or the tumbletrack.) try to land with your torso upright.
The logic behind this drill is if you can land sitting upright, when the mats are gone rotation and gravity would have pulled you back down to your feet. It forces you to set, because if you start your rotation before setting, you will faceplant the crash mats/resi pit (which doesn't feel good.)
For reference, here's the other thread.
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Good luck