Modbus IP Persistent connection and RTU Together Problem

[savaskorkmaz]

Hello,
We have an energy monitoring project with the following setup:

• 36 Modbus RTU Energy Analyzers connected via 5 Modbus RTU to IP converters
  
• 4 Modbus RTU Rooftop devices connected directly to the LM5 RTU-1 port
  
• Each energy analyzer has approximately 90 data points
  
• For the 36 energy analyzers (via RTU/IP converters), we are using Persistent Connection
  

My question is about performance:
The Rooftop devices connected directly via Modbus RTU are extremely slow — data updates are almost not coming at all.
Could this behavior be caused by using Persistent Connection for the 36 energy analyzers?
In other words, can persistent connections on the Modbus TCP side negatively affect the polling performance of devices connected on a separate Modbus RTU port?
What would be the ideal communication settings for this kind of project on both sides:

• Modbus TCP (RTU/IP converters)
  
• Modbus RTU (directly connected Rooftop devices)
  

Any recommendations regarding polling intervals, request grouping, persistent vs non-persistent connections, or general best practices would be greatly appreciated.
Thank you.