No, this is completely on me, you’re right. I shooed off this issue into the evasive parenthesis about assumptions. But were I to try to spell it out — and again, maybe you’re right that it’s in the book. I don’t have it to hand and can’t off the top of my head remember — I guess I would say something like this.

The rent you can charge and the overall price of a property are proportional: more expensive price, higher rents. That this needs to be so is easiest to see in cases where people buy a property with a mortgage to rent out: if they buy a more expensive property then they’ll have a bigger mortgage and so if they’re relying on rental income to pay the mortgage they’ll have to charge more rent.

The assumption I was making was that something akin to this point holds generally. I think that’s a case that one could make, but I don’t know how to make it, so you were right to flag it.