Hi Karol,
Please find the response below.
In Gantt currently milestone task are rendered with start date value with respective to left corner of rhombus.
As per your request we have logged improvement task to render milestone task with respective to center of the rhombus with start date value.
These changes will be done and included in our upcoming volume 4, 2017 main release which will be expected to out at end of October, 2017.
Thanks,
Suriyaprasanth R.