Correct, the frequency that the data is created is in the hands of the device, that data is passed to emonhub via serial and emonhub forwards it, it does have a “throttling” feature to limit the number of http requests made to the server, ie if the device sends every 5s, this could be buffered and posted in a single “bulk” upload every 30s, this is predominantly to help emoncms.org’s load and also to help with latger setups, even if you have (for example) 10 emonTX’s sending every 10s, by resticting the send interval to 10s would mean all 10 payloads are sent in one bulk upload every 10s rather than 10 requests each 10s.
Can we assume you are still using original emonhub v1.2? (ref Help with RPICT w/ Atmega Controller - WARNING Device communication error - check settings). What setting have you tried and where is it located? The default setting is actually 0s so by not defining interval = 30 or similar in the http reporter (original emonhub has reporters, the emonpi variant has a http interfacer)
If you look at emonhub.log you should be able to follow each received frame of data through the process to the outgoing http request. Maybe there are some illegal chars that cause emonhub to discard some frames?
Just to reduce confusion, “polling” is a term that is used when one device or software requests or interrogates a device or software for data, ie the “polling” device is in control. Your device is in control, it “posts” or “sends” it’s data when it chooses, emonhub simply listens and acts on data as and when it comes, your device is in control, it isn’t being “polled”. HTH.