The diagram that I drew yesterday in relation to leaning trees was about as wrong as it could be!!!
DON"T CUT IN THE WAY SHOWN IN MY DIAGRAM!!!! 
Here's how my bad diagram should have been drawn......thanks to Bigshea for prodding my lazy bum into correcting it...apologies to all for the original which was too hastily drawn and basically got things arseaboutface.
Remember this is for forward leaning trees, with a significant lean, and the intention is to avoid a barberchair.
Though I will admit that when I do this type of felling cut I cut the strap in line with the plunge not as far below it as shown, I will make more effort to make the final cut below the plunge as shown in the diagram.