FYI, on Sunday eve, with half a tank, handling was pretty good. Lateral grip seemed better too, though 9c temp - I'm veering towards the opinion that it's just all the salt on the roads at the moment... we had rain, and they didn't re-grit.

Getting back on topic though, as the fuel dropped to 1/3 to 1/4, I felt that I could feel the affects of sloshing. Admittedly I was trying to provoke by deliberately setting up a resonant left-right wave in the remaining fuel slosh. After several small left-right-left steering inputs, I'd return to the straight ahead and hold the wheel firmly. I swear I could then feel two tugs on the steering, one to the left, and another to the right. Both seemed to be step impulses, which leads me more to the fuel rather than tyre hysteresis explanation.

Additionally, though I might be imagining it, when going round a fast left bend and twitching the steering (Ie, follow the curve in a series of step corrections, rather than smoothly), there seems to be more of an impulse force hitting the right side of the car than when you do the same thing on a right hand bend. This might be something do do with the shape of the tank - the fuel filler being on the right hand side of the car.

This is all very much my own musings - I may be right, I may be barking up a non-existent tree, it may be more noticeable because of my current tyre setup... who knows! I'm still learning. I must attend a driver ed track day sometime!