I had the seat on its lowest position and found it adjusted quite well for a tall guy like me. The back of the seat I had fairly upright since that is the position I prefer driving in. I am 186cm high and about 85kg and the seat was supportive enough. Fuel filler cap I would not know about, I just pulled the open lever and the attendants filled up.
With regards to the i10, I would only take the 1.25 and not the 1.1 and there are two reasons for that. First is the power, the 1.25 has 64kw and after driving the 60kw Spark I would not settle for less. Second reason is the 1.1 i10 does not come with ABS so emergency stops could result in a more serious emergency.
The engine rev limit and gear ratios did make overtaking easy, you can reach 140km/h in 4th before it will cut the power. I felt more confident in this car than my previous long distance trip from Cape Town to Kleinzee (Springnbok) and back in a 6 speed 1.3 Corolla with 74kw on tap. I had to shift more frequently and the engine cut out a little too soon for my liking.