There's a setting in the options for tactical battle thresholds. If you want to always be offered to fight or not, set it to 0 or 1, otherwise if fewer units than the threshold are involved in a fight, it will autoresolve. The default is 4 or 5.
I could not find this option on the options screen. I could be missing it I suppose but I feel I have been very thourough in checking the option available. Are you talking about editing an ini file or something? If so what is it called and what's it's location?
