How about "Depending on the tube, between 1:1 and 1:2 ratio."?
https://hps.org/hpspublications/articles/allard.htmlRatio of N-16 Gamma Response Relative to Cs-137
GM Tube Ratio Comments
N1002/8767 1.88 Through mica window.
N1002/BNC 1.90 Through mica window.
N1003 1.96 Through mica window.
N201 1.71 Through 0.047" SS wall.
N205 1.90 Through 0.010" SS wall.
N210/BNC 1.58 Through 0.109" SS wall.
H220/7840 1.90 Through mica window.
N107 1.61 Through 30 mg/sq.cm SS wall.
N112 1.65 Through 30 mg/sq.cm SS wall.
N114 1.73 Through 30 mg/sq.cm SS wall.
N115-1 1.09 Through 80 mg/sq.cm SS wall.
N115-1S1 1.42 Through 80 mg/sq.cm SS wall with high Z filter.
N116-1 1.24 Through 80 mg/sq.cm SS wall.
N116-1SE 1.63 Through 80 mg/sq.cm SS wall with high Z filter.
N117-1 1.74 Through 30 mg/sq.cm SS wall.
N1l7-1S 1.73 Through 30 mg/sq.cm SS wall with high Z filter.
N118-1 1.03 Through 120 mg/sq.cm SS wall.
N118-1S 1.49 Through 120 mg/sq.cm SS wall with high Z filter.
N302 1.76 Through 0.020" SS wall.
N305 1.82 Through 0.010" SS wall.
N305S 1.99 Through 0.010" SS wall with high Z filter.
NP315-6 1.52 Through 0.020" SS wall, platinum plated inside.
NP334-6 1.48 Through 0.012" SS wall, platinum plated inside.
NP358-6 1.69 Through 0.009" SS wall, platinum plated inside.