This is the most informed post that I’ve seen on the INTENSITY control [from Russ Wedelich – Eventide]:

https://www.eventideaudio.com/comment/20065#comment-20065

Dan Gillespie – Eventide describes INTENSITY as controlling feedback in the Phaser / Flanger algorithms:

https://www.eventideaudio.com/comment/12049#comment-12049

It’s worth mentioning that the new per-preset WET / DRY routings can separate your input & processed signals; irregardless of the current INTENSITY value. You will need an external device – or multiple amps – to remix them to subtle proportions, though.  But there may be another option open to you.

When I need similar effects mixed to the far background (and I’ve been doing that much more here lately), I’ve been turning to the Delay and Pitch algorithms.  Many of them have a MIX or WET MIX control, some type of modulation, short delays, and feedback routings.  You can dial in just a hint of phase, filter, and flanging FX.

Here are a half-dozen examples of that concept: