Thank you for your very comprehensive comment!
Since this was our very first entry to any game jam and doing so in a completely new environment and engine there was a lot for us to learn. This lead to many unexpected issues we had to resolve before being able to implement ideas for ramping up the difficulty unfortunately.
Once voting is over I will implement the changes to the beam which you suggested and an increased difficulty as you get further. It might even include whumans which are trying to shoot down the Ufo ;)