This is a four-in-hand with a dimple on a straight collar:
Note that the straight collar's vertical length means that even the four-in-hand (the longest of the major tie knots) itself can't reach the collar's tips. I think this would look unbalanced. The dimple allows you to vertically extend the knot component of the collar-knot visual unit such that the knot seems to be a natural growth downward from the collar rather than a little lump visually dwarfed by the collar.
I disfavor the dimple on larger knots (like the Windsor) for the similar reasons. The Windsor, with a spread collar, is big and broad enough to carry the collar-knot zone. A dimple almost looks busy.
To form the dimple, tie and tighten as usual, but right before the last two or three tugs on the front blade finalize the knot, make The Trident (TM) with your dominant hand--
--and insert the index finger under the top layer of fabric on the knot, then pinch the outer edges of the front blade with your thumb and middle finger, then pull. Repeat until the knot is as tight as you want it.
Bonus: Valet Magazine has a photo spread of all the men's fashion shows from NYC this week. You can click on each designer's name to see more photos. Scan through it to see if anything catches your eye, and then work that into your wardrobe.