I'm a little confused about this. A full power DTV channel bleeding out an existing analog channel?
A regular NTSC analog broadcast channel requires a 6MHz slice of broadcast spectrum. As part of the DTV transition local broadcast stations were allotted another 6MHz channel for those DTV broadcasts. The data in the broadcast can identify the channel as a ".1" subset of the existing analog channel even though it is really a completely different channel number. So a station taking its DTV channel up to full power should have no effect at all on the existing analog broadcast. It will cost the station more money in terms of transmission power.
When the analog channel is shut down the station can choose to move the DTV signal to the space formerly occupied by that analog channel and then give up the spectrum it was using temporarily for its DTV channel.
Anyway, that's my understanding of it. For instance, I can pick up KDFX channel 3 in Wichita Falls, TX in both analog and its full power DTV version. The station can't squeeze both broadcasts into just 6MHz of spectrum.
Not sure I'm quite following you. But YES, digital channels can interfere with analog. Consider adjacent channels, and the waveforms are somewhat different. Somewhat different characteristics. This interference possibility has been the subject of a great deal of review by the FCC & others, and is not fully understood. There are unknowns in the transition, and a staggered out transition simply increases the chances of problems cropping up.
And to clarify: The digital channel may be transmitting on, for example, the spectrum identified as channel 47. But it will appear to the viewer as the good ole' channel 7 (for example). In that 6 MHz of bandwidth, the primary and ALL the subchannels of the digital signal are carried. I wouldn't say the digital channels and subchannels are a "subset" of the analog channel. This can only be confusing to many folks.
I think the problem is multi-faceted. First, they don't really know how well the interference problem has been solved- both for digital to analog (for however long they may co-exist with only some digitals "moving") and even digital to digital. Also, many digital stations will have LOWER power after the transition. That, and propagation (reception) differences with digital, will likely result in many people losing OTA reception, or being obliged to move to a rooftop antenna. Perhaps in coming years, some of these digital stations will increase power, if it can be shown to not cause interference, and to be in their interest. Or if they're coerced. Personally, I believe they should be forced to cover AT LEAST as many OTA households after the transition, as they did before. I suspect these "OTA" stations often just want to sell to cablecos and satcos, and dump their OTA expenses entirely.
BTW, just for general interest, after ATSC was set and well along in the process of stations starting to commit funds to the system, another hybrid system was developed. It supposedly demonstrated a way of combining the digital and analog signals in the same 6 MHz, but was certainly not compatible with ATSC or the equipment people were already buying. And I don't think it allowed for HD until after the analog was dropped, IIRC. It was stillborn. Wish I could remember the name of it.