Picking a IM volume plan for 2020-21

I’m doing IM Kona Legacy spot in 2021. We are not sure we have to do a validation race yet but believe we have to. I’m in for IM TX 70.3 and then Kona in October. I might do a 24 hour adventure race in March “for fun”. I am 59 yrs old and Kona will be my 20th IM. Being my age I’m concerned about recovering adequately. I likely will pick between Low Volume or Mid Volume plans. Here is my Q: If I start with Mid volume, but, am unable to hit my intensity targets, is it better to drop down to Low volume instead to hit targets better instead of the slight increase in volume but missing my intensity targets?

Why are you struggling with your intensity targets? Is it because of recovery or can’t you hit them recovered either?