Suggestions for aerobar risers height/size

I've recently bought a pair of used Profile Design T3+ as I wanted to try having a different resting position. I already have a pair of SQLab Innerbarends, but after a 2500km bikepacking trip I've realized that it was not enough, especially during long flats. Additionally I'd like to try an ultra-distance event, thus it felt like a reasonable purchase.

At the moment I have a Surly Bridge Club. Given its geometry the aerobars require some rising to keep the position consistent. The riser kit comes in different sizes/heights, from 15mm up to 70mm. From a very basic stationary test using pieces of woods, I found that the rising should be between 50mm and 60mm.

Given the nature of the test, the (felt) difference between the two is minimal. I would buy both if they weren't crazy expensive (a pair or risers is around 50 euros, more than I'd paid for the aerobars). Obviously I could always return one, but I feel it might take some time riding to assess how comfortable the position is.

My questions are therefore the following:

1. Is there any specific "rule" that I could follow in setting up the aerobars height? Many other rules I've found in a blog post by Torsten Frank. Anecdotal evidence is also appreciated;
2. I would assume that a slightly higher setup could be better than a slightly lower setup. Do you have any experience with that?
3. I was also thinking about 3D printing some samples, but depending on the material, I don't know if it's safe at all to ride with them (even briefly);
4. I've seen that Profile Design pads come in both 16mm and 20mm thickness. I currently have the 16mm ones. Would it be worth it to get new ones? I prefer riding off road, I assume the 20mm might provide some extra padding. Could the 4mm eight difference help me with the 50mm/60mm indecision?

I "fear" that I will end up trying one and eventually buy another if not comfortable enough. Either way I'd appreciate if you have any suggestions. Perhaps it can be helpful to others as well. Cheers.