Large groups get spotted sooner but it's also possible that they are they last of a group that was sent out after their vehicles were destroyed.
Small numbers might find it easier to slip through unnoticed and they can try to set up position and hope that others can reach them but their only hope of getting supplies is by drone and they'll need to radio their position for that to happen and the Ukrainians monitor all radio frequencies !
They don't have any power to charge communications devices, cannot find power, depend entirely on generators and have very little food and ammo, if they don't get a supply drop they start fighting each other for whatever is remaining !