I am not sure if you have 4 motors or 2, but if it I 4 then it will have more power so can accelerate faster so when you drive into someone you are moving faster so get more engagement. By having 4 motors you can also gear for a higher top speed as you have more power and by having more power the bot will reach a higher speed anyway as it isn't limited so much by not having enough power to move the machine faster.
If you only have 2 motors then forget what I said, just double up the wheels at the front so you have plenty of grip and save yourself some space as weight from the 4wd setup. But I get what you say about trying to keep the essence of the machine- perhaps you could accept this is a different design and come up with a new name rather than going for an undesirable design for traditions sake?
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