The consumption for vanilla beacons should range between -80% and +140% with vanilla modules and default settings. Could you provide more details to help me replicate the issue? Which mods are you using?
Depending on your mods, some beacons with more module slots may not use modular power with default settings. Variations are created for beacons starting at those with the fewest module slots - if a beacon's variations can't fit within the entity limit, it won't get any variations and will function normally. You could increase the entity limit setting to cover more beacons, or adjust the other settings to reduce the number of possible variations.
Also, make sure the beacons have had a chance to update - they're normally updated over time, but you can mouse-over a beacon to force it to update once your cursor leaves the beacon.