2x sim phone - problems making/receiving calls on smarty 4g-volte

A Smarty SIM does not need an active data connection for 4G VoLTE calling to work.
VoLTE (Voice over LTE) operates separately from mobile data.
As long as VoLTE is enabled on your phone and supported by SMARTY, you can make 4G calls even with mobile data turned off.

I appreciate how you may have interpreted my post to be discussing how mobile data usage might affect the calling. Let me rephrase my question::
Does the smarty sim not having data enabled at all and the priority being for data connection to be using the second sim affect volte calling?
In my experience and testing, the answer is yes.

As I said above from my testing, there is a significant problem when the data package in use is using the EE sim not the smarty sim. When I change data use to be smarty, this problem appears to go away. Coincidence not.

Would you care to address the specifics of secondary sim being used for the data connection and how they may affect the smarty sim being able to use volte?
I see from googling that this appears to be a problem experienced by others on other networks leading me to think it's a limitation of volte - along with my experiments.

Just keep in mind that your phone needs to support VoLTE and be compatible with SMARTY's VoLTE service.

Let's just put a cork in that one. My phone is compatible and it's correctly setup with VoLTE enabled. Which by the way is working fine with the EE sim. The smarty list isn't well maintained.