GNU Radio loop bandwidth normalization From GNU Radio documentation, the control_loop block proposes loop bandwidth values in the range $[\frac{2\pi}{200}, \frac{2\pi}{100}]$ in radians per sample.

Some blocks, like the new timing symbol sync block recommends a value around $2\pi\cdot 0.040$. Given sample rate $R_{sample}$ and symbol rate $R_{symbol}$, the symbol rate can be expressed in radians per sample as 

$$2\pi\frac{ R_{symbol}}{R_{sample}} = \frac{2\pi}{N}$$

where $N$ is the oversampling ratio is samples per symbol. From literature, the loop bandwidth around a few percentages of the symbol rate (say 3% for example) is recommended.

I have a problem in relating the recommended control_loop values to the values suggested in the literature. Suppose for example the signal is oversampled by a factor of $N = 100$ samples per symbol.

A loop bandwidth value of say $\frac{2\pi}{100}$ will be equivalent to 100% of the symbol rate, which doesn't seem to be logical. The same loop bandwidth will be equivalent to 3% for an oversampling factor of $N = 3$.

I think that the ratio between the loop bandwidth and the  symbol rate depends on $N$. For example, in the figure below, I don't think a loop bandwidth of $\frac{2\pi}{100}$ would mean the same thing to the FLL and the PFB ($N = 4\,\text{sps}$) as it will to the Costas loop ($N = 1\,\text{sps}$). 




Why don't the recommended values in control_loop take N into account?
How can the loop bandwidth in GNU Radio synchronization be configured
as a percentage of the symbol rate?
I can only answer your second question:

"How can the loop bandwidth in GNU Radio synchronization be configured as a percentage of the symbol rate?"

The tracking loop in the symbol synchronizer block operates at the symbol rate, estimating timing error and making a correction once per symbol.  So the sample rate of the error signal from the TED is at approximately 1 sample/symbol.  (I say approximately, because technically the block is continually estimating symbol clock error and adjusting its estimate of the symbol clock period, but its objective, nominal operating rate is 1 error sample/symbol.)

This means that in terms of normalized digital radian frequency, $\omega T_s$, for the loop filter, the symbol frequency corresponds to $2\pi$ radians/symbol.

The loop bandwidth parameter of the symbol synchronizer block is expected in units of the normalized digital radian frequency.  So when one specifies $\dfrac{2\pi}{200}$ for $\omega_n T_s$, one is specifying an approximate one-sided loop filter bandwidth of $2\pi \cdot 0.5\%$ radians/symbol, a one-sided filter bandwidth that is $0.5\%$ of the symbol frequency.

To express the loop bandwidth input of the symbol synchronizer block as a percentage of the symbol frequency, just use

$$\mbox{(one-sided) loop bandwidth} = \omega_n T_s = 2\pi \cdot n\%$$