... Add to the fact that while the Red Army in 6/40 would be smaller than 6/41, it won't be attempting a massive expansion either that left units disorganised and poorly equipped in the first days of the war. ...
I've been translating Merekovs account of the mobilization of the Red Army & he describes a fairly hefty expansion from mid 1939 through 1940. The original record seems a bit muddied by the existence of multiple directives for expansion, and overlapping plans, and possibly out right Maskrikova or deception. It appears the Red Army expanded from approximate 100 organized divisions mid 1939 to approximately 180 divisions during 1940. This did not spread the existing trains cadres as thinly as the 300+ designated division HQ of June 1941 but it did water down the command and staff quality. Problems were aggravated by two reorganizations of the armored or mechanized forces, and a misguided neglect of artillery training. After the Polish campaign there was a decision, made at the top, that only tank and airfares mattered & infantry or artillery obsolete and high levels of training for those arms not urgent. At this point in the summer of 1940 the skill level of the commanders and staff were not so diluted or out of synch as a year later, but there was still some decline.
The record for the frontier fortifications is a bit less clear. Some accounts I've seen suggest that pressure from above, to move the fortified zone forward, resulted in the weapons, communications, and other infrastructure in the old zone being dismantled in haste & the weapons ect... transported forward long before construction of the new positions started. If this is true, then at least parts of the old defense zone may have already been rendered impotent.
Similar problems were emerging with the air forces and support echelon. That is between expansion and displacement forward into Poland a not trivial degree of degradation of capability had occurred by June 1940. While not as catastrophic a loss of ability as in 1941 there was still a decline in tactical and operational ability.
A German assault in 1940 would be constricted to the region of land between the Baltic States and Hungary ... It probably grinds to a halt somewhere between the Stalin line and the D'niepr river. ...
More important than where the German army halts are its losses relative to 1941. Consider:
Germans.......vs West...vs USSR
Divisions.........122.........134..........91%
Casualties.......155k.......213k........67.1%
Div, avg loss....1270......1590........79.6%
Enemy Div.......140.......183..........76.5% (Note the 183 Div represent the number deployed vs the Germans 22 June to 7 August. Not the total in the Red Army)
Casualties per..1107.....1160.........95.4%
Enemy Div
The table is from Randal Reeds analysis of the 1940 campaign.
The basic intent of this table is to demonstrate that German losses during the six weeks long campaign in France were in fact roughly equal to their losses during the first six weeks of fighting in Russia a year later. Not shown are the figures for Allied and Russian casualties for this period, since they are unavailable. The French however seem to have lost some 500,000 men prior to their surrender (KWP). Russian losses, as nearly as can be determined, ran to at least 750,000. Thus the French with but 66 percent of the casualties suffered by the Russians, inflicted losses upon the Germans in direct proportion to those inflicted by the Russians. All figure are approximate. with independent regiments and brigades being lumped into "divisions".
Without nitpicking Reeds 47 year old text... The point I am taking from this is, in 1940 a somewhat less diluted Red Army may very well inflict larger losses on the attacker. That is the total casualties may be higher, and spread across fewer divisions. That can bring the losses in infantry closer to the crippling or effective level sooner than OTL. ie: 213,000/122 = 1745 casualties avg per div. The equivalent of two entire battalions per div lost, and then some. Since the highest portion of German infantry losses were among the NCOs & company grade officers this level of losses starts to cripple the small unit leadership & can badly degrade combat power beyond the raw numbers.
While the much lower number of Red Army units avail be against the Germans in 1940 is lower it must be understood the attacking mobile forces are half those of OTL 1941. Ten Armored and five motorized divisions, if none are left in the west to counter the French. Vs the 20 armored divisions actually deployed in 1941. Thus even against a smaller Red Army the ability to execute three or four massive mechanized thrusts does not exist in this ATL. At best there is the wherewithal for two weaker mobile axis of attack. This means encircling or killing 700,000+ soldiers in six weeks will not occur. Quite possibly not even half that.