If the attacker chooses not to attack the protected target, then the ability has worked without any dice rolls necessary. Job done.
I see what you are getting at - the idea is that either the target is harder to hit, or the EK becomes the target - yet at the table I found how the mechanics unfolded, leaned toward wanting Defense. Before I got my Plate, I didn't have the strongest AC, so being targeted all too quickly depleted my hit points. Or I would throw
Shield, but an EK is limited in casts, only 2 or 3 for a big chunk of their career in the average campaign (tier 1 and 2). Fortunately my DM allowed me to switch to Defense fighting after a few sessions made the shortcomings clear. Again, this is at our table with our specific party. Once I had stacked Plate, Shield and Defense, I was being hit rarely enough that
Shield become really telling, and I could stay in the fight and continue to hold back foes. I felt like I presented as appealing a target without Protection, as with it.
In our other game, I saw our Fighter having a better time. He had Protection and the DM largely ignored it, meaning that every so often he'd happen to be in the right position to use it, and it counted. "Every so often". What I observed is that always-on +1 AC would mechanically have served him better.
A couple of other things to consider:
Use cantrips and spells to appear more threatening. e.g. Minor Illusion, Enlarge (can also enable you to block a passage).
Good idea, but aren't you then protecting by actually blocking access? So Protection can't help you, and Defense would be great! (In that scenario.)
Have a poor charisma. Try to negotiate with the hostiles and accidently insult them instead.
When I DM this does not work, because if a player wants to use their words to shape foe actions, they need to succeed, not fail, in the appropriate social skill. For me, to do the opposite devalues the abilities in question.
I would allow this scenario, but the EK will need to
succeed at a Charisma (Deception) ability check, contesting the target's Insight. I would likely give the target advantage in most situations, or +5, to account for their hostility and suspicion.