Bob H,
Nice Job on box wedge. Let me state 1st. that I in no way am an expert. I also have a large box wedge splitter. If you continue to have issues with material getting stuck I would suggest to change the angle of you bottom plate at the out feed end. On my splitter I have approx. 4" at cutting side and 10" at table this will limit friction with the horizontal blade. Much like the TBWL w7. I would also try to set the middle vertical wedge at 90 deg. as you did, but the additional vertical wedges I would suggest to install with bottom of the wedge set at an angel away from the center wedge vertically. Kind of like an upside down "W". 4" at the top and 5" or 6" on the bottom 5" down from the main horizontal blade. I have found that as the wood splits the upside "W" angle of the secondary wedges force or direct the wood down the wedge thus limiting the friction and in my case falls out. Your wood wont come out square but I have found it to be helpful.
Hope this helps