Measuring current vs voltage
Answer

Your Transimpedance Amp, TIA,  feedback RC=T values must match the source RC values for best results.  The spectral voltage gain, the impedance ratios are matched ratios for the broad-spectrum flat response.  This is like tuning a scope 10:1 probe for a square wave response.

Other info

No long skinny ground leads are allowed as this adds a potential LC resonance > 10MHz ( usually around 30MHz) which is usually outside the OA bandwidth but might not. This is a common fault using scope 10:1 probe with excessive ground clip inductance.  Ground L=1uH/m approx gives series resonance with cable 100pF/m approx. Your values may vary.

Consider a  source is a piezoelectric (PZ) charge crystal for example of known C and G=1/R leakage and cable is a known impedance with typ. 100pF/m depending on impedance and type.

The BNC connector C is negligible ~1pF compared to cable capacitance, but any motional change in the cable will vary C some xxx ppm (  parts per million)  which will appear as a piezo effective noise so the cable must be semi-rigid not standard RG58 for lowest noise.  Perhaps double braided stiff RG58 taped down is OK with special low pF coax as we used for crystal accelerometers.