Hi Russell. Pics would help if you could. I don't really understand why you have a wider cut at the bottom if your blade is at 90 degrees side to side. Are you able to check the squareness of the blade to the table when the blade is at the top of its stroke and again at the bottom of the stroke ? It seems as if the top or bottom arm of the saw is moving sideways as it moves up and down. If the blade moves slightly out of square front to back as it moves up and down should not affect the width of the kerf at the bottom but if the arm or saw blade itself moves side to side as the saw is cutting it will affect the cut causing the piece to be removed to not come out either up or down. A couple of issues could cause this situation - the bearing or bushing in the arm is worn allowing side to side movement, or the blade is not centered in the blade clamps ( that is, the top or bottom of the blade should be moved , if possible, by adjusting the clamp so the blade is centered in the clamp .
When you say the blade is not 90 degrees front to back I think of a C-arm saw where the blade actually tilts front to back in an arc as the saw blade moves up and down . This is the way a C-arm saw works because it only has one pivot point at the lower back of the C- arm.
I hope this may help you. I have no experience with this saw. I have run into this kind of problem where the blade is not centered in the clamp at the top or bottom and adjusting the clamp , possibly at both top and bottom , may be required to get the blade centered and sawing at 90 degrees side to side.
Garry