If you want to kick him, probably just a bit shorter than your whole leg. If you want to punch him, then you can probably do it just fine if it's not too close or too far away.
If you're talking about engage distance, it doesn't make that much of a difference. If you feel like you're too close, you can push Uke away before hitting him, and if he's too far away you can just get to him and do some cool acrobatics on your way.