The ing/strelky/Gds battlegrpoup is a deliberate hardcoded feature from Relic; to keep the game from ending too soon. An example of it is to be found in the market garden campaign, the first Valkenswaard scenario. If you lose all your PGs a battlegroup will be spawned, probably until such time as a FHQ is built in the church.
CatFishy is right about the T1/2/3/4 build order and the spamming but I think he is incorrect about AI preferences. I think the AI will build at least one each of all units in a given tech level, (probably with a 50%VG, 33%MG, 16%sniper probability scheme for the next unit to arrive). This process seems to be interrupted when a higher tech level building is completed. At which point a new probability scheme is implemented until one each of the T2 units is built, one of the probabilities in the T2 probability scheme possibly allows for a backTeching unit build. When the AI selects a doctrine a similar scheme is initiated.
At some point, around when T3 is built the Spamming starts and the AI selects a unit type that it seems to keep on building. I think the spam priority switch uses the resource pool reserves to select what unit is spammed. An AI propaganda Spam will usually be NI until Katyuskas come out when it may switch to Katy's (IIRC Katy's are cheaper than NI's). I occasionally see it happen with LWGd and Wirbelwinds and rarely nashhorns. It is also seen sometimes with Partizan/KV2 spamming.
My favorite AI Spam is one faction spamming Storms and another faction Spamming Stu42Hs. A good challenge! LW spams are the most pathetic AI spams, Closely followed by straight NI Spams. Partizans would be second worst but that Spam is often changed to a KV2 Spam.
The IHT/2 PG/Shrek seems to be a bonus to the AI. Target the IHT to get the PGs to bail out ASAP. Whats worse I think the Shrek squads may always have two shreks. Anybody know for sure?
I play AI at hard and expert levels. The AI schemes I have mentioned above are not gospel. They are my best guesses. If we can get Robotnik involved in this discussion we may get more solid answers.
孫 TheEF_v1.7.10
子 ArtIllegitimi non Carborundum -"Vinegar" Joe Stilwell
兵 ofSun Tzu says: In warfare one compels and is not compelled by others
[b] 法 War