There's a 4/5 effeciency rate on power supply, as the beam itself is consuming some of the energy (regardless of what combo you use.)
I didnt see if you had mentioned it, but you must also have power capacity on those reactors (and their carrier) to get the full potential regen (otherwise excess power generated is essentially dispersed into space), preferably give yourself some buffer space to allow for lag spikes.
I notice that your making a central core of power reactors and shelling it in the beam blocks, however, doing the opposite will give you more effeciency in your reactor block usage, likely cutting down the overall end size a bit compared to this current model.
Another issue you might be encountering is the repeating logic might not be keeping pace with the rate of energy generation, you'll want to adjust your combo to account for that. Hope my insight helps.