Making the portal area wider would be a bad idea, as placing portals already is quite restrictive due to the large area the portal has to cover. Also, changing the bbox size of the portals would mean changing how the existing portal maps play, and change their records. Not a good idea.
But I get complaints about this ever since ai's portal model got added. Maybe the model should be made a tad smaller to fit the portal's box again?
Indeed: this is the case. Maybe intentionally by ai, maybe not, we don't know. You now have to hit the INNER area of the portal, hitting its border will no longer teleport you:

1. Open Notepad
2. Paste: ÿþMSMSMS
3. Save
4. Open the file in Notepad again
You can vary the number of "MS", so you can clearly see it's MS which is causing it.