I am not sure I completely understand but if you are shorting shares you Own, it's the equivalent of selling them.
Afterall wwhy pay interest on a short position when your losses increase as share price drops whilst your profit from shorting increase = neutral and your paying interest.
If however you sold then as the price drops you save losses on you long and when you buy back you have in effect got more unit for your investment = the equivalent of profit from shorting . Although you can't see it I your portfolio.
I know my platforms behaves like this, I only have buy or sell and selling stocks I do not own is shorting.
For tax purposes you could short using a different platform but in that case you are shorting shares you don't Own and woild need to cover it by buying back as a buy order. So 150m shorts will always be 150m buys.
An interesting question, anyone have a different view?
