I am successful in getting past the big enemy through that terrain now. Note the game didn't expect me to skip a few pixels, and a piece of terrain in the lower-left corner isn't loaded properly.
It's not just position, but angle as well. I did crash into the ground at the same X-position in a few different attempts, but if I'm going to the right at some speed, it won't let me through. Left motion or no X motion seems to work. For the most part, doing this kills my momentum, but it still looks faster than killing the thing and bouncing once. More careful comparisons still need to be done, however.
One attempt through the tunnel. The horribly jagged ground looks to be nearly unavoidable. As for the bounce off the ledge near the small wormhole, I might want a higher angle than that. Picking a different method is also a possibility.
Fuel also looks to be a concern. Would like to keep the pod intact past the second big enemy.