Based on my 2 week audition, I thought that the T51P's bass tended to do that a bit (at least compared to the DT1350's). I'm surprised though that you feel that the HD25 Alu is looser than the T51p's (I haven't heard the HD25 Alu, but based on impressions I've read about them).
I did about the same as you, but the "pinprick in tape" mod is pretty in-exact at best lol. A bigger hole probably would have worked out better for you. Then again, you are enjoying them most without the tape at all, so I think you found your answer!