Interchangable? H4i, H3i humidifiers on S8's

Before I get to my question, let me head off the clarification that I know the parts of the h3 and h4 aren't themselves interchangable.. there's an upgrade kit required.
But I have two S8 blowers, one with h3i and the other with h4i humidifier. I am wondering if I can/should swap the humidifiers? They look to be completely compatible in the electrical and pneumatic connections. In fact they appear to work when swapped, at least somewhat.
Now I can report that the older AutoSet Vantage does not have h4i as a menu choice -no surprise there, but I'm thinking the only real difference is the reservoir capacity and how the lid seals to the reservoir.
Anybody else been down this path before? Thanks in advance for your thoughts. earl

You can use either one on an S8. My new S8 Autoset II doesn't have the setting for H4 either. I do like the H4 much better though.