Decreasing percentage yield

I’ve distilled to batches of sweet grain over the past month. The set up is always the same – I boil at around 160deg. about 4 inches of sweet grain in 4 gallons of water. I then transfer to a fermenter (6 Gal glass jar), add 5 lbs of sugar and shake the hell out of it till the sugar is dissolved. I then wait till the temp is around 75 deg to add the yeast. (I use Red Star Champagne yeast).

It pops off for about 6 days or so – then stops. I transfer that thru a double filter into my 15g keg. I use a 2″ tower. I have packed the bottom of the tower with copper packing. I cook it outside with my propane burner. I have a Home Depot bucket for ice water that pumps into the top part of the discharge on the tower – and the bottom part is where the ice water is discharged.

I always dump the first 100ml – then I get great, clear shine at around 55% (+/-) for a quart. Then I get around 50% for about a quart – then it dropped to around 35%, then worse.

What am I doing wrong to not get 55%+ for a full run?

Thank you in advance. Running for hours and hours for a quart of good clear shine is rough.

Rob