You can have as big or small a position as you like (with respect to your margin balance, which is in turn based on your chosen leverage).
As you add or remove to your position, you just see the aggregate position to date. Your P/L is only realised when you close out a position fully.
If you reduce a position then your base price changes to reflect this. It's just the way margin trading is implemented on there.
Right, so in this implementation, selling a partial position (when going long) results in a lower base price, rather than any realized P/L. It still has a purpose, namely helping you prevent your position from forced liquidation.
I noticed that it was deciding which shares to sell for me and adjusting my base price... it sold the highest-priced long shares first, which was fine, but this should be explained ...
As for 'positions', though - I don't get the definition of 'position'... I only saw one position reported on the Trading page, but in History it reports multiple positions being liquidated although I never cashed all out.
As far as I can tell, you only log profits once you have completely cashed out of all 'positions'.. is that correct?