Looking at this jetpack, it used more RF (6,800 RF/t) in flight than other Tier 5 jetpacks (850 RF/t). It was also not possible to change the RF used in the config.

can confirm for version 1.12.2-2.2.20.0

if my math checks out, it seems that instead of dividing I:gelidEnderiumEnergyUsageBonus by 100, you are dividing it by 10

assuming all values are default, we have:
integration{I:gelidEnderiumEnergyUsageBonus=80}
tuning{te{jetpack_te5_enderium{I:energyUsage=850}}}

850*(80/10)=6800
850*(80/100)=680

here are some screenshots just in case

one potential workaround is to divide I:gelidEnderiumEnergyUsageBonus by 10 in config, but then the tooltip would look weird

actually, scratch that, cuz I just tried changing I:gelidEnderiumEnergyUsageBonus from 80 to 8, and now energy usage is now at 0 RF/T. Are you perhaps not using a float value for the multiplication result?

ok, last resort, I'm gonna set I:gelidEnderiumEnergyUsageBonus to 100, then set energy usage to 680
...uuh... nope...? still at 6800 RF/T

hmm... what about energy usage set to 68?
yup, that did it! so the temporary workaround is to set rate to 100, and then do math on the jetpack's energy usage rate itself

hopefully this excessive explanation will help solve this

@h3oCharles do you mind checking the 1.16.5 version for this same issue?