Yes, Khan was surprised by the shields going down and reluctant to admit that he had lost what had been a significant advantage.
But at the beginning of the engagement he couldn't have known he'd gain that advantage. Certainly he hoped to catch Enterprise by surprise, but it was a very real possibility that Enterprise would raise shields as Reliant approached. Khan's overconfidence manifests there in his belief that he will gain the upper hand against an experienced captain and (what he must assume is) an experienced crew.
My point at the end of my post was that Khan is so bent on revenge that it is pretty clear that when splitting his forces he would give the order "nobody but me kills Kirk," which would explain why Tyrell didn't immediately kill Kirk.
But at the beginning of the engagement he couldn't have known he'd gain that advantage. Certainly he hoped to catch Enterprise by surprise, but it was a very real possibility that Enterprise would raise shields as Reliant approached. Khan's overconfidence manifests there in his belief that he will gain the upper hand against an experienced captain and (what he must assume is) an experienced crew.
My point at the end of my post was that Khan is so bent on revenge that it is pretty clear that when splitting his forces he would give the order "nobody but me kills Kirk," which would explain why Tyrell didn't immediately kill Kirk.