But if too many locals leave then a liquidity crisis is created,which is what has happened so market conditions,depending on your strategy,make it hard to secure that tick.
The algo-funds are really just giant market-makers so even if you don't see them as competition they see you as theirs.They are bid and offered all day in every month and every spread hoping to do trades that you want to do and force you out of your position and then eventually,the market altogether.
Couldn't say if they had anything to do with reversion to full-tick,if I had to guess I'd say the full-tick would be better for them but they are BIG players in Euribor and Eurodollar too which are half-tick so they are perfectly capable of adapting.I actually think they've switched back because so many locals left,more than they could have imagined and they're starting to panic.Combine with their share price collapsing and they're probably worried about getting laid off,believe me,they've done what's best for themselves and self-preservation,not to cheer up some disgruntled locals.