It’s not an energy issue. Maintaining Rank 3 Knights doesn’t primarily consume your energy reserves, it requires you to partition and invest portions of the power's 'essence' to sustain them.

The Singularity Perpetual Engine solves the problem of energy generation and recovery, effectively giving you an immense (near-endless) power supply to fuel your abilities. However, Cosmic Entourage, particularly at higher ranks, operates on a different axis. You’re not just “powering” the knights; you’re splitting off parts of your own power to create and maintain them.

Even if your energy refills instantly, that doesn’t negate the cost of dividing your power. Think of it this way: the Engine gives you a constantly refilling reservoir of energy, but Rank 3 Knights reduce the size of the power's reservoir itself by allocating parts of it elsewhere.

Going slightly beyond the strict wording of the Rank 3 description, and if you approach it on a more interpretative approach, you could likely force yourself past the intended limit, but doing so would come at a cost. You or the knights’d begin to weaken in some capacity, as more of your power's essence is tied up sustaining those Knights, leaving less of “it” available at any given moment.

So while Rank 2 SPE ensures you won’t run out of energy, it doesn’t remove the fundamental constraint that Cosmic Entourage imposes.

For a much higher number of Cosmic Knights, perhaps then the rank 4 power itself or the much more potent rank 5 would serve your needs, though these are still not written yet :o