Cyclic Sleep transmit only - misunderstanding?

Using two Series 1 modems, X-CTU, and an FTDI USB/serial cable. One modem “local” 100% default config. Other modem “remote” has one ADC channel enabled, and:

ST=500 (msec)
SP=1500 (15secs or so I thought)
IT=3 [samples before TX]
IR=100 (msec)

Result: “remote” modem wakes up about once a minute (not 4 times/min as configured). The Assoc LED on my breakout board blinks, and indeed 3 ADC samples received and shown on XCTU Term window. Config confirmed by re-connecting it to XCTU.

Question: Is this behavior due to the “local” modem having no data queued for the “remote?” At this stage I don’t need any data to the remote, just sensor values transmitted from it, through “local,” to microcontroller.

Thanks for any advice & education!