Straight corners -- start your cut by inserting the blade partially into the matboard an inch or so early while moving the cutter, then press down the rest of the way at your starting mark.
I found it was the initial pushing of the blade into the matboard that would deform the blade -- then as one starts the cut the blade would straighten out and give one a curved start. By starting the cut early while drawing the cutter forward keeps the blade from deforming. Works with 4 and 8 ply.
That is a great sounding suggestion. I never tried that. I do have my technique down with the dexter/logan combo and can make perfect cuts. But I have quite a lot of logan blades to use.