Thanks!
You never know...I do not have a Bitfinex account, but you can do real BTC shorts there, as far as I know, so would have been possible...
Do you know what ?
If I had been doing real margin trading on Bitfinex, I'd have probably lost out because I opened the "pseudo-short" around March 21st following a huge rise from 0.013 straight to 0.018. But then the market went against me 2 days later and continued right on up to 0.024.
If I had had collateral at risk I'd probably have panicked and bought back in at a loss. As it was, since the BTC 'collateral' was still in my own hands I could just re-contextualise it as a profit take and kiss that Dash goodbye (since I was only trading with a minority holding). That gave me the courage to stick with the 'plan' which ultimately is now working out.