Should I book an oversized luggage seat on Shinkansen if my suitcase is *just* barely below 160 cm?

I know that 160-250cm is considered oversized.

I just measured my larger suitcase and it is just 154cm, so just barely below the limit for oversized but I feel like anyone seeing it would assume it is oversized and think I'm trying to get away with not paying for an oversized luggage seat.

Should I just reserve an oversized luggage seat to be safe? Or am I just being paranoid? (I do have a tendency to overthink things 😓).

Also if I did get an oversized luggage seat but my husband only has a carry-on, does he have to sit in a different area, since he would not have oversized luggage? (Never been on the Shinkansen, or to Japan, before so not sure how that works.)