I use HEQ5 Pro with EQDIR-BT dongle with PHD2 and have recently made some changes to EQMod driver for this purpose. The original code didn't take into account communication delay with the mount which is around 50ms per command when using BT and around 16ms when using EQDIR cable and 32ms when using PC Direct mode via the hand controller. This made each pulse essentially that much longer. Also the code used timer for all pulse lengths which made short pulses quite unreliable. Last issue was that if mount status query timer happened to hit during the pulse duration, the pulse got significantly longer as command to end the pulse got delayed. These issues should be remedied by current EQMod driver version from nightly which added configuration items to ignore very short pulses and configurable limit how long pulses are handled synchronously. The value for minimum pulse should be around the communication delay so 50 ms for BT, less for wired connection, the default value of 10 ms is very conservative. Default value for timer threshold (100 ms) is probably good as is, but I've used slightly longer 150 ms as the limit myself.
As for the guide rate I've settled on 0.5x after testing 0.3x, 0.75x and 1x, it seems to be a good compromise between correction speed and not over correcting. I'm not sure what you mean by minimum pulse rate, I use 3s exposures so PHD2 does corrections only every 3s to average out effects of seeing. Sometimes I use 2s or even 1s, but 3s has proved to be good compromise.
I tested with Jarno's changes yesterday and everything worked fine. Of course, I didn't have issues before (using EQDir cable, so latency wasn't much of an issue), but the results are great nonetheless!
Unfortunately this doesn't have any direct impact on dithering with PHD2 as such, only that the dither pulses would be more accurate than before. For me dithering seems to usually work, though at times Ekos doesn't seem to register settling signal after dither, but resumes after timeout anyway. More rarely PHD2 doesn't seem to receive the dither command from Ekos at all so there seems to be some fragility with the communication between the two.
I don't think it has ever worked better for me than it does now (which isn't perfect but usually enough), it was much worse before Robert's changes some time ago and I've used PHD2 with Ekos for about two years now. Anyway, it would be nice to figure out the issue and fix it for sure
in the meantime, I got the calibration process completing and autoguiding is up and running. However, the RMS looks poor, around "10". Maybe this is due to mechanical reasons, the telescope has a high imbalance on the DEC axis, as the telescope is heavy on that side, where the ccd is attached (I need to resolve),
Something went wrong with the csv file creation, so I guess that may not help. Could someone kindly have a look at the log file, to see if there are any errors that could contribute to the high RMS?
(the guide cam is off axis, and I am guiding via the EqMod, not ST4)