When it comes to setting fields for spinners I am a massive fan of 'in, out' fields from the start. Who says you can't attack with men on the fence.
We regularly start with 2 close catches on each side, slip, gully but have boundary riders on the off and legside (probably deep cover and mid wicket).
I am also a big fan of leaving square leg open to encourage the sweep shot. There are few batsmen at our level who can play it regularly well and sooner or later get it wrong and are LBW or top edge etc..
Completely agree, I would argue a man on the fence at deep midwicket is in an attacking field position for an offie, especially in T20 matches.