Unless there has been major changes in the way it operates since FraktalUK put it in KSPI originally, the impact experiment does not work the way you think. Biomes are meaningless to it. You basically land several landers, ideally 6 to maximize the science value, on the planet. One near each pole, and 4 equally distant from each other along the equator and then start crashing things into the planet. You can repeat it but after a few the science goes to nothing and you have to transmit the data after each impact. There's no data loss in transmitting but it takes *a lot* of electric charge power to do it, so I recommend putting several batteries and RTGs on the landers if you cant go nuclear with them.