@McD This ones mainly for you as I saw you looking for tips on this the other day.
And lo and behold in this months Sound On Sound the editor (Paul White) wrote a great piece on rolling your own Shimmer reverb with Logic stock FX. I can't copy/paste all the content here but I can post an excerpt from the intro (which is publicly available), and a few screenshots that fill in the blanks. The stock Logic FX are nothing special and any of them can be replaced by the great options available on iOS. And the results will be richer and offer more control than the simple 'Shimmer' reverbs currently offered on the platform.
Here's the intro:
Shimmer reverb is, at its simplest, a reverb tail that has been shifted up by an octave, although other intervals can also be useful on occasions, and sometimes the octave reverb is mixed with normal reverb. However, getting it to sound as smooth as the output from a high-end pedal requires more than just sticking a pitch‑shifter after your reverb plug-in. The better shimmer pedals may also add in some filtered delay with lots of feedback, EQ and even compression, so setting up a dedicated effects chain that you can save as a user preset is the way to go. If this is something that you think you might use a lot, you should also add it to your default song template.
The full article is made public after 6 months or if you really want the detail now you can purchase the article for the princely sum of £1.
But as I mentioned above, the images paint the proverbial 1000 words. However, spend the £1, it's really well written and will help you take things a little further.