Actually, you can drop far more than that and still be in VO2max range. Even dropping as much as 10% is still in VO2max range (assuming a 120% of FTP VO2max setting).
Here is a pic from my sheet showing the actual % of FTP with Workout Intensity adjustment ranges.
Keep in mind that VO2max is a range from 105-120%. More important, also remember that 120% is not an appropriate percentage for all riders.
The most important thing with VO2max work is to maintain an very high level of oxygen uptake. This is best done with manageable, but demanding intervals that can be completed at the prescribed duration.
Coach Chad covered this in his 2-part deep dive on VO2max (I need to find the episodes for reference). But the big takeaway for me was that the breathing and cardiovascular demands are more important to this training than the particular power level used.
As such, people should experiment, especially if they are unable to complete the VO2max intervals at the full duration. You lose more by bailing early than by decreasing power. You need to maintain high demand of you aerobic system, and hopefully complete the final intervals in the sets with significant breathing demands.
As to reduction amount, look at the prescribed duration of the work intervals, consider the impact of the Workout Intensity reduction based on my table and consider you history with VO2max work in the past.
I feel it’s s best to under-shoot the first couple of intervals if you have known issues. Then increase as you get into it and make sure you know how you are reacting. As long as you are finishing each interval, and the full set properly spent and breathing hard, I suspect that you are well into the range you need to be.
Be willing to push it up. But avoid the levels that have you not finishing full intervals and sets. The final 1/3 of each interval, and the final set are very important to the VO2max goal.