Evaporator size for cold trap

Hello guys, I'm trying to design my own cold trap with R290 refrigerant to build a freeze dryer. As we know, the lower temperature the better, however I've done some testing with a blast chiller and the freeze drying process works well even starting from -20/-25 C, however I'd be happy to reach at least -35 C with my project. When the lowest temperature will be reached, the cold trap will have very little termal load and for this reason I'm worried about compressor floodback. To build the evaporator, I have the option of using 6mm copper pipe in spiral around a steel pot, for a total length of about 20 meters, or a 8mm pipe of a shorter length because less coils will fit in the same external area of the pot. Even if the termal load is the same in both cases, I'm assuming that the 6mm solution would be better because tha liquid refrigerant would have more time to change phase before it reaches the compressor, am I correct? Thank you!

You could always include a suction line accumulator to prevent liquid reaching the compressor
https://www.parker.com/literature/Af...cumulators.pdf

suction line heat excannger...

or a heat exchanger between the high and low side?

can make one did eith a pipe in a pipe system?