The bets to which Rule 4 deductions apply will depend on the time of withdrawal. If a horse is withdrawn at the start then, assuming start is imminent and a new market can’t be reliably formed, the Rule 4 deduction would apply to all bets. If it’s early enoguh for a new market to be formed then the deductions will be be made on bets at board prices struck before the withdrawal. If you typr Rule 4 deductions into Google then the deduction scale shoudl be easy enough to find.
I haven’t bet on early price markets very often but I assume that bookmakers apply Rule 4 based on price of horse at time of withdrawal with deductions made from bets struck before that point.
Betfair make a deduction on bets before withdrawal based on amount of money bet on the withdrawn horse.
Simpler with the Tote. All they have to do is taken the money bet on the withdrawn out of the pool calculations.
Rob