This article covers one scenario: a lead booker selected Pay full cost, and other players — including members — have joined the booking. The lead booker's cost stays the same.
Why it works this way
Discounts follow payment, not attendance. Since only the lead booker pays, joining costs a player nothing and commits them to nothing.
If member rates lowered the total here, joining would become a way to cut the price rather than claim a spot. A lead booker could ask one or members to join, bring the cost down, then have a non-member play in that spot. The member never plays and never pays, and the club has given a member rate to someone who isn't a member.
Payment is the only thing the system can verify, so "Pay full cost" is a fixed price.
Important mention: The lead booker still gets 'their individual share' discounted if they are a member or belongs to a special cohort.
How to get individual discounts instead
Book with Pay your part. Each player then pays their own part at their own rate, so a member gets the member rate because the member is the one paying for that spot.