It depends on the price. I think mine was about 1-1/4" when I bought him. I was looking at him trying to remember. He is about 1-1/2" now, so than may be right. So, 1" may work. One thing for sure, it won't be aggressive to the larger and will absolutely accept the other's dominance, so it should work.
BTW, I just noticed my female has a huge swollen belly. She is very healthy, I wonder if she is gravid or pregnant? I don't even know if they lay eggs or live bear. I guess I best be finding out.
EDIT: I haven't researched yet, DAUH!, if they are A-sexual they have to lay eggs and milt them. He won't have a "male member". Family forum here.