I don't know if that has ever been defined...
When I think of deep stops, I consider that to be any stop deeper than half of your absolute pressure. I.e. if you have a 40ft stop on a 100ft dive, or a 130ft stop on a 300ft dive.
Depending on how long you are diving and big of a deco obligation you have, you may well have a couple stops deeper than half your absolute pressure. Let's go to 300ft for 30mins on 12/70 with deco gases of 35/25, EAN50, and O2. 10ft final stop and GF's of 60/70.
Total of 161mins of deco, but only 6 of them are below 130ft and start at 160ft. 99 of them are at 30/20/10. 3.7% below half pressure, and 61.4% in the final atmosphere.
If we do that dive on VPM 0 which gives about the same amount of total deco at 163mins.
Stops start at 220ft and 17 of those minutes are below 130ft. In contrast the 30/20/10ft stops only have a total of 65 minutes. 10.6% what I would consider deep and only 40.4% in the final atmosphere.
A GF of 10/95 gives a comparable ascent for this dive profile however that does not necessarily mean that 10/95 is comparable to VPM0. Since they are different models the GF equivalents shift depending on the specific dive profile. Point of that though is to show that 60/70 has essentially an identical TTS as 10/95 but the stops were distributed differently.
The ascent curve with VPM is much flatter as the distribution of stops is more even. Play around with planning software so you can see what they do on profiles more similar to what you are doing, above was out of Deco Planner for reference.