Splitting profit jointly owned commercial property

Husband and wife, new client, own a unit that is rented out as a hairdressers salon. The property is owned jointly. She has some employment income that uses up her PA he has a small pension of about 5,000pa so doesn’t use all his PA. Previous accountant allocated all rental profit to the husband so no tax was payable. My understanding was that with a jointly owned property the profit was deemed to be split 50/50; certainly with a residential property. Is it the same with a commercial property or is there an ability to vary the split with a commercial property. Client have said the property is jointly owned there isn’t a separate and different split of the beneficial ownership