Yes the energetic would be absorbing ALL the damage from the troopers in a radius not just 5, I used 5 troopers as a reference point for the 20m range. The main thing to note is that currently energetic causes you to take 2 damage a shot regardless of the weapon, the only spike to this is the christmas sniper which makes you take 8 damage. NPCs rarely have perfect accuracy and don't have unlimited ammo as a whole, they can fire about 35 bullets before reloading and do about 100 damage each if all of those bullets were to hit. Taking that down, the Sentinel would be dragging most of the aggro anyways so realistically the ability would still be AS effective as it is now, it's just about taking the damage off those stray bullets that sometimes kill off a low HP trooper that is seconds from healing while also not making the entire situation straight up OP.
Also, don't think of the powers as independent things, if you have a Guardian walk in, cast valor, a Sage battle meditating and a Sentinel using energetic shell. The troopers can push even heavy fire because of the combination of powers with very little casualties. It just means that a GM can pace the events by throwing absolute armies at us without us just dying on repeat. Plus it means we can handle harder skirmishes, so long as you can organise the troopers around the Jedi.