@Lubliner: He had two exposed flanks. He adjusted for the left by having to "refuse" - which then created the vulnerable salient in the middle (pick your poison) but did nothing about his right (or about the significant gap in his front that resulted from his lack of enough troops to man his line). He significantly increased the distance from any support for his now-isolated corps. I don't think we have any idea as to what he "anticipated" or, if so, whether that made sense. It's complete speculation. All the problems were created by his decision to move
unilaterally - despite even Hunt's advice when Hunt left to check with Meade.
As I keep saying, all anybody has to do is look at an accurate map of his second line position in relation to the rest of the Army. I still await the opinion of a military professional that the second line was a good idea. That's completely different from whether he somehow blundered into a location that Longstreet, et al thought was open. And anybody who thinks that Sickles knew the intended location and direction of Longstreet's attack is actually going farther than even good old "Historicus" went in his pr campaign. It should come as no surprise that his corps was wrecked and that - despite his post-battle spin - the day was salvaged on the Union left by Meade, et al slamming in troops from the V Corps and the II Corps.