Icom IC-7100 Low power on 15m SSB

I know a lot has been written about the LP problem, but I use mainly digimodes and I can get very nearly full output in that mode from every band EXCEPT 15m, when I can only muster a max of 25-30w out. Sliding the souncard volume up and down has almost no effect on power in this band, only ALC moves with it.

Also when TX the rig draws about 22A for my 25w (on 15m) whereas on other bands the current is much much less for 80-100w out.

On a different antenna I can reach 40w out but no more, which suggests antenna 1 (a vertical) is not resonant at 15m, which I can accept, but antenna 2 (OCF) is. Again, on that antenna altering connector settings and sliding soundcard volume up only increases ALC, not power. If I go too low then obviously the power starts to tail off.

Anyone clever see a relationship between the high current and low output?

BTW I use HRD+DM780, in the soundcard properties I have 16 bit 48000Hz DVD quality, and all enhancements off. I DON'T run digimodes at full power, this was just an experiment to please don't lecture me about smoking my finals on a 100% duty mode!