Ian, I have to say that my experience with Perceptol and ID11 is quite different from what you describe. A few years ago I did a whole series of tests with various developers. I used 35mm FP4 and HP5. I chose 35mm because differences would show up more readily in the final prints. The tests consisted of exposing several rolls of film on the same subject in constant light, then clipping off short lengths of film and developing them in various dilutions of Rodinal, Xtol, ID11, Perceptol and Pyrocat HD.
I won't describe all the results, but one thing I did find was that there was no difference in the finished prints between ID11 at 1+2 and ID11 at 1+3. Ditto Perceptol.
I found that FP4 looked great in Perceptol. And for 35mm FP4 my standard practice is to use Perceptol at 1+2. Or 1+3 for film exposed in contrasty sunlight. Pyrocat HD gave results very like Perceptol. Equal sharpness. Equal fine grain. And equal lack of compression in mid-tones. The latter is very important as it gives a sort of "peaches and cream" look. Definitely not bland.
I preferred 35mm HP5 in dilute ID11, as it gives the grain a bit more bite than you get with dilute Perceptol. And my standard practice with HP5, in all formats, is to develop it in ID11 at 1+2, or 1+3 if exposed in very contrasty light.
I had previously used Rodinal quite bit. It is supposed to be very sharp. But my tests showed me that, in fact, it isn't as sharp as ID11 1+2. Dilute Rodinal is also supposed to work well as a compensating developer, i.e. it holds the highlights back whilst allowing the shadows and mid-tones to develop fully. My tests showed that dilute Perceptol, dilute ID11, and Pyrocat HD all outperformed it in this respect. Rodinal mid-tones were compressed, and shadow detail wasn't there. But it was grainy! I even tried Rodinal semi-stand, i.e. 4 initial inversions then one inversion every five minutes. This was claimed to increase the compensating effect, and keep up the film speed by bringing detail out in the shadows. But this turned out to be another internet myth.
Doing these tests was hard work, but worth it. I now develop everything in ID11 at 1+2 or 1+3, except 35mm FP4 which I develop in Perceptol 1+2 or 1+3.
Alan