EHT generator.

[ppppenguin]

If not one of the biggest enemy's to a EHT winding is the self capacitance of the winding.
Keep it low by winding narrow coils with many layers as you have done and keep the number of turns that make up the EHT winding to a minimum
The trouble with using fewer turns is that you will require better insulation between the layers.

Once it comes into effect no matter how many more turns are put onto the EHT winding the EHT voltage wont increase. In fact put enough on and the voltage will decrease.
It is possible that your EHT winding is suffering from self capacitance. The only way to know for sure is to remove some turns and see dose the voltage drop.

This is why diode split LOPTs work well. You're using the capacitance to good effect. Needs small and reliable EHT diodes to embed in the LOPT.