Trask's method of determining Max Black (an old friend of mine...) works well if you don't take the term too literally. You really need to be sure you don't go too black.
Black is an interesting thing on photo papers. The shoulder of papers means that you can see very small increments of increasing black with added exposure for a long, long way. To achieve a true Dmax on paper requires much more exposure than is really practical when printing. You need to find, instead, a satisfactory deep black for your clear negative density that keeps you from having to overexpose your film three stops from published speed to get shadow detail (when proofing as you describe, which I do as well).
That said, the principle is correct. Expose film edges till they are as black or very close to as black as the exposed paper beside them (as you seem to be doing). I would say that this part of your method is right on.
However, before you go twiddling with EI, make sure that you examine the shadow values in your negatives closely. If the shadows are not printing as you like, i.e., they do not have enough detail, then, yes, lower your EI and expose more. If, however, the shadows have adequate detail, it is just your negative contrast and you need to increase development time or print on a higher contrast grade of paper.
Using a too-fast EI is by far the more common than underdeveloping. Most manufacturers' development times tend to be a little too long in my experience. I imagine you will end up rating your film a bit slower. However, do check shadows first for the following reason.
The contrast of the scene affects the highlights if you are proofing your negatives as you describe. Low-contrast scenes will have good shadow detail and dull highlights if developed to "normal" when proofed this way. Conversely, high-contrast scenes will have good shadows and blown-out highlights. This is not necessarily bad!
I use the Zone System for sheet film, and develop each sheet for optimum negative contrast. For roll film, however this is not practical. For roll film, my adage is "expose for the shadows, develop "normally for everything, print for the highlights." This means, find a development time that allows you to print a "normal" contrast scene on grade 2 or 2.5 paper (the smaller the roll film, the higher contrast grade paper you should standardize on. Some 35mm shooters standardize on grade 3. This helps with grain.) Find an EI that gives you shadow detail you like and a development time that puts "normal" highlights in the proper place.
Keep in mind also that if you use an averaging meter, you are not really "exposing for the shadows." If you are using an in-camera averaging or center-weighted meter, you should go ahead and use the camera meter reading for all normal and low-contrast scenes, but
overexpose a stop for high-contrast scenes. This is counter-intuitive, but ensures that you have adequate shadows in high-contrast situations, when the meter might severely underexpose them (since the "average" reading of the scene is so high).
At any rate, if you have arrived at an EI that works and a standard developing time, your "proper proof sheet" will tell you what contrast grade paper to try: contact prints with good highlights print on your standard contrast grade, ones with overexposed highlights print on lower contrast grades and ones with underexposed highlights print on higher contrast grades.
Bottom line: You need to determine your EI and development time yourself, for your equipment, materials and tastes. Manufacturers' recommendations are just starting points. The "proper proof" is a good tool to do this with. Keep printing negative edges black and adjust your EI and development times to get where you want. Expect low- and high-contrast scenes to have highlights that are "under- and overdeveloped" respectively on the proof sheet. This you take care of with paper grade.
Hope this helps some,
Doremus Scudder
www.DoremusScudder.com