Cum Variable in VLT calculation problem

On : 12.2.4 version

I have a problem in the VLT calculation , assume an operation consists of 3 activities , each activity has its own resources.

the problem is , those three activities normally work in parallel. so if each activity should produce 88 CRT/HR for example,
the three activities still should produce 88 CRT/HR.

from the log file attached you can see these data

(1079)Recipe=6633 Item =405822 routing_qty=88 fixed_lead_time (U)=0 Cum Fixed=0 variable_lead_time(U)=.0014224
Cum Variable=3 Lot Size=88 Daily Work Hour=23.966

the variable lead time is driven from this equation
variable_lead_time = (Cum Variable /Daily Work Hour) / Lot Size (3/23.966)/88 = .0014224