iPad and iPhone endpoint problems, timing sync (Roon 1.5 build 339 stable 64 bit)

I’m having a problem with both an iPad mini (latest version) and iPhone 7+ (running iOS 11.4.1) when using them as endpoints:

Problem: The speaker delay (in Speaker Setup) doesn’t seem to have any repeatable/reliable effect (often no effect) and timing is often way off (my estimate maybe up to 100 or 200 msec) between the iOS devices and other endpoints (usually 2 USB connected directly to a MacBook Air, OS 10.13.6, and one endpoint connected via a Sonic Orbiter). Usually I listen to my iOS devices while they are close to me and while my other endpoints are playing at a significant distance. So I want to put a speaker delay for the iOS device of maybe 800 to 1000 cm. The iOS device timing sometimes seems to change with this setting, sometimes not (usually not). I have also tried making my iOS device the highest priority device for Clock Master Priority of the group in Device Setup (with other endpoints set either manually to a lower priority or “default”. None of this seems to matter. I’ve read from earlier Roon posts from I think Brian - to make the “worst” clock the highest priority so that the other (better and more stable) clocks will follow the less stable one that likely drifts more. I still can’t seem to ever adjust the iOS device(s) to match the timing of sound arrival of the other endpoints (that are maybe 30 to 40 feet away). And worse, the delay seems to shift randomly so maybe this is some limitation in the iOS device as endpoint? I imagine the iOS device doesn’t have a super stable clock, but putting it as the highest priority clock should resolve this. All devices are on the same 802.11ac local network, very high throughput, no bandwidth/throughput limitations, good signal strength, etc.

I know iOS devices are just newly supported as endpoints and I really appreciate this feature functionally and sonically but unless this time sync issue can be resolved, they won’t be very useful to me except when I don’t use them in a grouped mode.

I really do love Roon in general, all the new features being added and functionality and I look forward to further enhancements all around and specifically with iOS devices (especially full featured DSP support on the iPhone).