I agree. You don’t want small groups booking your place at a lower rate if it means missing out on a larger group who is naturally willing to pay more in total. With a cleaning fee of $140 I’m assuming that there’s not much difference in your cost if someone uses more beds than you’d expect.
As to how many to include in the base price, there are pros and cons to both options. If you set the base price for 6 people and have an extra charge beyond that, some will try to sneak in the 7th or 8th, but others may be less likely to assume that it’s okay to bring an 8th or 9th guest. If you include 8 in the base price with no option for extra charges, some will assume that they have the right to bring as many guests as they want because they’ve rented the whole house.
I have a place that sleeps a maximum of 8 (due to local bylaws) so I set the base price to include 8 people and don’t allow any additional guests. People still try to weasel their way into bringing more, whether it’s a baby in a portable crib or adults with an air mattress. I used to have the base price at 6 and $50/person/night beyond that, but found that I was better off raising my price $100 a night or more during peak periods, and during low periods I tend to get smaller groups anyway because people can afford to have a little more space when prices are lower.