Is there less 'drop' with an implant exchange? (photo)

At 18 days, there is still going to be swelling of the soft tissues. I would not make any final assessments regarding your ultimate position for at least 2-3 months. Based on your photos, I am slightly concerned regarding NAC position but this should improve to some degree as your implants settle. I think that a strap for now is reasonable but speak to your surgeon about these issues and I am fairly certain that over the next few months they will improve. 

Much will depend on exactly what was done during the procedure.  "Dropping and fluffing" (a process wherein breast implants round out the lower breast poles, and the breasts overall may may appear to be larger as breast implant "settle") may not necessarily occur with revisionary breast surgery.
For example, if the breast implant capsules of the  lower breast poles are incised (capsulotomy),  than some breast implant movement ("settling") may be expected over the course of the first several months after surgery.
  Your plastic surgeon who will be your best resource when it comes to accurate assessment of concerns, advice, and meaningful reassurance or predictions.
 Best wishes for an outcome that you will be pleased with long-term.

Hi and welcome to our forum!
It depends upon exactly what procedure was performed. If a simple implant exchange (same size and position), the pocket walls are only minimally disturbed. As the walls are mature, I wouldn't expect much change in position of the implants. On the other hand, if you also underwent capsulotomy or capsulectomy, where the capsule is incised or removed, one would expect a degree of implant settling over several months.
Discuss your procedure and your concerns with your plastic surgeon.
Best wishes...