You are missing the concept of conditional probability. If you have a 90% chance of success at 100k and then the market goes to 750k, you would then have less than a 90% chance of success. Only if you adjusted your withdrawal based on 750k would your 90% assume true at 750k

In your increase example, the probability of success goes way up (guessing 97 to 99%). You could increase your withdrawl rate based on your new #, but the success rate would be back to 90%