[Diabolical Artificer]

That sounds good, a bit of HF boost is handy,the opposite is often the case. You might need a tad more capacitance so could try a 220p or 330p with your varicap in series, I've attached a quick guide to give you some idea as regards square wave testing.

What I've found is at lower frequency square waves you can dial in the FB cap to get a nice sq wv but at 10khz might have to trim it back a bit. It is an interesting exercise though to do this, tweeking the capacitance & watching the response change.

Lastly a bit of a faff but you could fit a switch to shunt out the FB cap to give you a crude HF boost,very handy to have for old ears.

Andy.