Control Systems: increase the number of M-circles on a Nichol's plot?

With regards to the nichols() function, is there any way to:

1. increase the density of M contours (after the grid has been turned on). For example, in screenshot, you might notice that the plot (blue) comes close to touching the 6dB circle but doesnt quite touch it. If there was only another (or maybe a couple of) intermediate circle(s) between 3dB and 6dB...
2. Make the dB values of the circles appear on them even when zoomed in. The question mark in red is actually a -3dB circle but because I have zoomed in, it is not visible.

Are there any ways to address these issues (through code or from the gui interface)? Thanks for your time!