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I do not have a Monarch, but a rough rule of thumb is that you can turn a taper almost as long as the 'rail' of your taper attachment without resetting the attachment. If you need to cut a longer taper, a little bit more work is involved. You would not need to change the angle setting at all, but you would need to reset the attachment in a new position on the lathe bed.
Abom79 has an excellent video on using the taper attachment on a Monarch 10EE lathe. You can view it here: https://www.youtube.com/watch?v=D4h-lfYpjh0 It may not completely answer your question, but should provide you with some good, usable information that is specific to your lathe.