Trim the 117
I sail the 133 but have experienced the same issues when I first started using the board. It is true that all of the variables ( mast foot position, harness line position, sail trim, boom height) need to be in harmony and I suspect some have found solutions by accident! Like most of the Isonics the board needs to be sailed with even pressure on both feet. The biggest single trim factor that impacts on the balance between your feet is boom height.........OK there are limits and other aspects of trim have to be right as well.
I do not agree with the comments about downhaul adjustment. Too little downhaul on any large sail will certainly result in too much back foot pressure and with the 117/133 short board length you lose the ability to go off the wind. I set anything larger than 7m on max downhaul all the time...just using outhaul to increase/decrease power. I think some may have noticed a difference in balance between the feet simply because the centre of effort of the sail has moved forward by releasing downhaul.
I think the other aspect of trim that helps get that balance between the feet is harness line length......you probably need to try longer lines.
Overall my suggestion would be.....lower the boom by about 30mm.......bring the mast track back slightly.......use the next size up harness lines............set your harness hook lower if it feels uncomfortable at first.