Never played strategus, but riding a sumpter horse alone, for 13 min sounds like a very weak move... Personally, i don't like running away from a fight, i rarely resort to this "tactic" even if i have a ranged weapon.
How annoying it must be to chase a lonely sumpter horse for 13 min
On the other hand, if there are no rules regarding this situation - I guess one have to take some ranged weapons into battle, like a hunting crossbow. I don't know how it works in Strategus, so I might sound ignorant.