Reverse issues on 904 transmission

The torque converter drains back while sitting. Then the front pump doesn't run in park. Soooo, I start my 67 in park, let it run a minute then switch off, shift to neutral and start again. Torque convertor fills while engine warms. This is how I avoid that short delay followed by harsh reverse engage. I will ad this the drain back isn't nearly so bad if I drive the car consecutive days. I suppose some do drain back faster than others.
I don't know the internal workings of a trans or what part prevents/allows torque convertor drain. If I had to guess... One of those little balls in the valve body not seating just right. So long as I know how to make it function for me, I don't worry about.