Switch off relay from Shelly1 with tasmota and PIR sensor after given time

Question

I'm using a Shelly1 V3 with Tasmota 14.2.0 and want to switch the relay with a PIR sensor (AM312). After reading PIR Motion Sensors basically this works so far, but instead sending MQTT messages I would like to control the relay without an external home automation system to have the Shelly working independent on its own.

So I adapted the documented rule

Rule1 on Switch1#state=1 do Backlog Publish stat/%topic%/PIR1 ON; RuleTimer1 30 endon on Rules#Timer=1 do Publish stat/%topic%/PIR1 OFF endon

to this:

Rule1 on Switch1#state=1 do Backlog power ON; RuleTimer1 30 endon on Rules#Timer=1 do power OFF endon

But I am not able to let the relay switch off with the specified time. Instead, depending on the switchmode, the relay switches off after about 3 seconds or after about 20 seconds, not 30 (or any defined) seconds.

I tested Switchmode to 14 with Pulsetime of 130 as described as also all switchmodes and checked the console log to see how many seconds it took to switch off after a recognized movement:

• switchmode 0: 3s
• switchmode 1: 3s
• switchmode 2: 20s
• switchmode 3: 20s
• switchmode 4: 20s
• switchmode 5: 20s
• switchmode 6: relay does not switch on movement?
• switchmode 7: 3s
• switchmode 8: 3s
• switchmode 9: 3s
• switchmode 10: 20s
• switchmode 11: relay does not switch on movement?
• switchmode 12: relay does not switch on movement?
• switchmode 13: 20s
• switchmode 14: 20s
• switchmode 15: relay does not switch on movement?
• switchmode 16: relay does not switch on movement?

I guess it should be possible to control the relay to switch off after a movement after a specified time, not the actual 3/20 seconds depending on the switchmode?

How could I achive this?

Using switchmode 14 and sending MQTT messages so the external home automation system switches on/off works but as said, I would like to do this independently without an external home automation system.