Phase II LFO wave shape

[Damonsan]

Hi There
I built the Phase II and have spent some time biasing the led brightness and waveform amplitude, but I'm not quite happy with the perceived wave shape. It seems to have an acute dark transition and smooth light transition in the waveform cycle (see pic), but I'd ideally want a smooth sine wave.

I've built a 'Tremulous Lune' tremolo in the past where you can play with the wave shape, and was wondering if I could bias the oscillation similarly in this circuit.
Any help would be much appreciated.
Regards

 

[Damonsan]

Update..
After confirming the LFO IC resistors were visually the correct value I've ended up swapping out the LFO IC from TL072 to RC4558, which seems to give the smoother oscillation I was looking for. So I think I've solved my problem.