G36 Air nozzle lengths. Specific to Gearbox or Hop unit?

[Asomodai]

Crossposted for more visibility.

 

I have been upgrading a JG G36 older generation. This had the original hop unit with the built in feedtube and a (Short) 24.3mm air nozzle. 

 

I replaced the Hop unit with the AirsoftPro G36 model with tube adapter. I couldn't use the original air nozzle because it was too fat to go into the rear of the hop unit and create a seal.

 

I replaced the Air nozzle with an AirsoftPro G36 25.2mm (Long) air nozzle as I assumed the reason behind the different nozzle lengths was due to the type of hop unit used. 

 

Unfortunately the new long type air nozzle will not move back enough to let a bb feed through.

 

Is the length of the G36 air nozzle actually specific to the gearbox rather then hop unit?

 

If so then I will need to get the shorter AirsoftPro nozzle and hop it seals with the hop unit bucking despite being shorter. If not then I may need to look at some other reason.