what's the secret to making a good robot in robocode

Im not saying my system is a particularly good one, it just shows that using relative GFs should technically be exploitable. What you are saying, knowing enemy will shoot at .5, is basically using a flattener.

I don't know, I think to me the definition of "exploiting" means you can use it to improve your system. Tweaking a random movement to have a non-symmetric profile could be an improvement. With surfing, your goal is to model the enemy's targeting data model, which is done correctly by assuming symmetrical GFs. It seems to me a surfing movement is already aware of the GF symmetry and taking it into account as best it can.

From the perspective of normal (relative to orbit direction) GFs, what it comes down to is that you'd have is a movement which alternates between GF 0.5 and GF -0.5.

It's true like you say that this could have some level of effectiveness against targeting systems that are using firing waves only AND are missing certain segmentation dimensions...

I would say it could be 'exploiting' yes, but I would also guess there are very few targeting systems you'd reliably trick with this. It seems extremely fragile. Your maneuvers to "arrange to alternate orbiting ..." would give away which of GF 0.5 and GF -0.5 you're heading to in certain targeting segments/dimensions (easy near-100% hit rate against it), and even without that, asymmetry in the result of non-firing waves would cause a lean toward one or the other, causing an easy ~50% hit rate.

It would be interesting to see a demonstration of what in practice would be tricked by it though.