Well, I took the advice and am checking on the stock for the T18-D12 Shape-1.2D tips:
The one the iron came with was a "Shape B" conical tip which I don't find as easy to use:
The "el-cheapo" iron I am used to has a slant-cut conical tip, a little like this "Shape C" one:
I'm sure with some more practice, the conical tip will become easier to use. I really do need to get some flux though - but have no idea what to get, or where to get it from (decent stuff) - any ideas?