HD2 vs HD1 lock?

I'm curious about something here. On both my in-car radio (Dual XHD6430) and my portable NS-HD01 and with multiple stations I seem to exhibit the same behavior regards to HD lock. While on the main broadcast the HD signal will go in and out regularly whilst on the HD2 channel it will hold the lock almost 100% of the time in some cases. Given they are sent down the same feed of 0s and 1s, both HD1 and HD2 should have similar lock characteristics. Is there any technical reasoning behind why this difference is there? I'm just curious about this. Seems to me if the HD2 can hold so well, the HD1 should behave the same when often it does not.

Thanks. That actually makes more sense now that I think about it. Though all things considered from what I have been reading, most stations run their main channel and a single subchannel at the same rates (48kbps/48kbps) and given error correction involves some bandwidth taken away from actual audio quality I wouldn't mind seeing some EC put on the HD1's to maintain a better lock and listen to a clean digital signal (albeit with obvious compression artifacts, but those I have heard on most HD2's aren't terribly bad to the point of not being able to listen and often times with the processing used I'd much rather listen to the HD2 than the HD1 based on the audio quality) with increased highs and clear lows.