Hi Alex, thanks for your reply.
I thought I would fit one of the new fan jets back into the brush (so now there's one of each on it) and you can clearly see the difference in the two spray patterns. I will take a photo in the daylight tomorrow morning and send it over if it will be of any use.
Like someone mentioned above, I thought it was just me at first. I thought I must have a dodgy set or something as I literally went through everything in my set up looking for pressure loss and leaks etc but soon came to conclusion it was the fan jets.