The inverto support has kindly answered my email and referred to the SAT>IP Protocol Specification found here: http://www.satip.info/resources. See page 44 for info on Positions.
The positions refer to the "selection of a satellite orbital position", like 19.2E, 13E, 28.2E, ...
In my case, only Position #1 AA works, so must be enabled. If only any of the other positions are enabled, I get no signal at all. Not sure why not, as 19.2E should also apply to them? On the other hand, it does not seem to harm anything, having them enabled.