What condition to use to avoid placing such small closure bets?
Thanks!, that means there's no way to limit how small bets to place when it comes to close a trade.
You could have a green-up rule that calculates the green-up stake manually, store the result in an SV and have a condition to fire if it's >=1.
I don't think Betfair mind you placing sub £1 bets as long as it's not your bread & butter stake. The T&C don't forbid placing small bets per se, they forbid placing bets with the intention of taking advantage of rounding up.