I’ve injected above the naval – not very much higher, but where there was still a layer of blubber to stick a needle into. I did find that the higher I went the more painful it was.
And, yes, I found that Lantus used to hurt sometimes when I put it in – but I could never really discern a reason for it hurting or not hurting. It wasn’t wildly painful so I didn’t really investigate further, but I do recall – as Stephen says – that it does have a more acidic base than, say, Levemir.