Well most books would tell you that 4 inches is too close. Four inches does seem a bit close to me, even for cats. Your post did not indicate if the cat stepped over the trap OR stood behind it and got the bait.
I really think you would be well advised to back the trap off so the pan was more like 8 inches from the lure / bait, put side guides and have a stick just outside of the rear jaw (between the trap and the lure). This pattern gives the cat a clear path to the pan, will force it to step in the clear spot just before the rear guide and the distance will cause it to take the extra step to investigate the bait.