I have an ICOM-725 (HF system, 100W output) connected to a MFJ tuner
and then about 120 foot feedline run to an antenna I made myself.

I can get the SWR on the MFJ tuner to read nearly 1:1, but the
transmitter display shows only about a 25% power output.

It occurs to me that the impedence that the tuner is "seeing" is so
high that the transmitter simply cannot supply the necessary current,
i.e., as with any voltage source that gets swamped.

Make sense, or am I barking up the wrong tree?

Thanks.

Thomas