This may seem like a small thing, but it's something we get a lot of questions about and where there's a lot of uncertainty. The gap at the lacing of oxford shoes. Here we go through how you should think about this, what is actually right and wrong, and what you can do to change the opening of the lacing.
How big should the lacing gap be?
Oxfords are shoes with so-called closed lacing, where the tongue is placed as a separate piece inside the quarters and the vamp. On these, a V is formed when the lacing is tightened, and it is how big the gap is, and whether there should be a gap at all, that many are unsure about.
The lacing coming together all the way is not ideal. Picture: The Shoe Snob Blog
To answer quickly and simply, a gap of between 0.5-1.5 centimetres is correct, although a little up or down from that may be ok. Then the lacing doesn't run the risk of ending up completely tight after the shoes have been broken in and often stretches a bit here, so you can't tighten the shoes properly and they get a little slack at the opening of the shoe. And if it's the other way around, that the gap is very big, then it means that the last doesn't fit your feet and the risk is that they will pinch and feel tight here, and not least towards the end of the day become uncomfortable.
Here is an example when the lacing on oxford shoes gets too big, and they are also perceived as a bit uncomfortable here by the wearer. Picture: Styleforum
In other words, it's mainly about the fit, as always with shoes that is what should be the main thing, even if it also means that they will be good aesthetically as well. A big gap that still doesn't feel uncomfortable is perfectly fine in our eyes, comfort should always come first. Many people also prefer to always have a small V on oxford shoes, even after they have been broken in. This is both aesthetically appreciated and allows you to know that also on colder winter days, for example, when your feet may be considerably smaller than at their peak on a hot summer day, you can lace them up properly. It can be an advantage to have some flexibility in both directions, so to speak.
Here's an example of a good lace gap on an oxford shoe.
On a pair of derby shoes, with so-called open lacing where the parts on which the lacing holes are located are placed on the outside of the tongue, which is part of the vamp of the shoe, this is not something that is paid much attention to. The opening between the laces can be and often is quite large without any problem, which is one reason why derbies are good for people with a high instep. It's only if the lacing closes completely together that there can be a problem, as you can't tighten the shoes properly then.
How can you adjust the lacing gap?
The simplest and cheapest way to modify how big the gap at the lacing on your oxford shoes is, is to choose how you lace the shoes. If you want more room at the instep, you can choose a lacing method that leaves as much room as possible over the instep, and conversely, if you are looking to reduce the space over the instep, choose a lacing that fills out some here.
A lacing called Boston two-step (or sometimes Straight European lacing) is a lacing that has many advantages, since it provides good pressure distribution and you tighten both ends roughly equally, while looking relatively good at the same time. It fills out the instep well, also good if the instep is a bit high.
Shoe shop lacing is a simpler lacing method that gives more skewed distribution in length between the ends, and does not distribute pressure as evenly, but is common from shops and which fills out over the instep area. 
If more room is needed over the instep, this is a good version, called Straight bar lacing. It looks very neat too, and leaves plenty of room over the tongue. Pictures above: Ian's Shoe laces
If the instep of the shoe is clearly too high for your feet, lacing won't help. A good solution then is to add a suede tongue pad. It's self-adhesive and is attached to the inside of the tongue of the shoe, and fills out the instep of the shoe very well and comfortably, so that the lacing keeps the foot tighter. A perfect product to fill out the instep of shoes.