How much room needed for bench spotter behind verticals?

I am going to pull the trigger on a home gym setup. Due to limited space, I am leaning towards getting a wall mounted "space saving" setup, which is essentially the front half of a 4 post rack anchored to a wall. I will get spotter arms for safe benching and squatting.

The product I am looking at getting (Titan T3 space saving wall mount rack) has 3 options for the horizontals between the wall and the verticals: 12, 18, or 24 inches

Because of the aforementioned space consideration, I was planning on getting the one with 12" horizontal pieces. However, if I ever got a training partner, or actually got my wife or kids to train, it might be nice to have the option to have a spotter for benching.

I am thinking that the 12" option will not leave enough room for an effective spotter. Do you think that the 18" option would be enough? Opinions appreciated!

Assume a 1.5" wide stringer on the wall, plus the 3" depth of the vertical piece of the rack, and at least a half inch for the J-hook. That means the 12" option would put the barbell 17+ inches from the wall. The 18" option would give 23+ of spotter room behind the barbell.

Realistically, I'll be training by myself almost all the time. However, I'd like to make the area a useful as possible.

Thanks again for the advice, I'm really looking forward to having a training space at home!

Steve