1) THE ANALYSIS
First, the following analysis strictly refers to German divisions and soldiers purely. Other Axis countries' figures such as Romanian's and Hungarian's are not included in these numbers.
Various sources cite different numbers regarding the total amount of German military casualties throughout the war, that range from 4 million to 5.5 million. We're going with 4.5 million, and we estimate that Germany suffered 3.5 million casualties by June 1944.
This source shows that the Germans had around 290 divisions in June 1944.
This other source -taken from a forum post which cites two sources such as Kroener and Müller-Hillebrand- has a wide array of numbers concerning German divisions and soldiers.
May-June 1944 German Manpower
East: 150 divisions, 2,500,000 soldiers
West: 58 divisions, 886.000 soldiers
South East (including Greece and Balkans): 25 divisions, total manpower strength 440.000 soldiers
Denmark: 6 divisions (no strength given, we assume 80,000)
Norway + Finland: 12 divisions, 250.000 soldiers
Italy (OB Südwest): 28 divisions, around 500.000 soldiers
estimated TOTAL: 5 million soldiers, 280 divisions.
Considering that the 1941 standard German Division consisted of 17,500 men, and that 5 million/280 makes 17,850, we're going to assume that the Wehrmacht had at its disposal, in June 1944, around 3.5 million men for combat roles arranged in 280 divisions.
Sources such as (1), (2) show that around 9-12 million men were mobilized for the Wehrmacht. We could estimate that 70% of this quantity relates to support roles (i.e. not translatable to HoI-MP), which leaves us with something close to 4 million.
2) THE PRESENT IN-GAME SITUATION
Current German MP assigned to Military (divisions) is 1785. That equals to around 1.8 million troops arranged in 267 divisions:
NumberOfDivs (of which X are brigaded) TypeOfDiv | Total MP = MP+(BrigMP)
171 (35) Infantry | 1780 = 1360+(420)
30 (16) Armored | 242 = 98+(144)
25 (4) HQ | 133 = 105+(28)
13 (9) Mechanized | 148 = 40+(108)
11 (2) Motorized | 114 = 90+(24)
8 Mountaineer | 120
6 (3) Paratroop | 96 = 45+(51)
3 Cavalry | 27
On paper, the 267 divisions should host 2660 MP. 267 divisions instead of ~280 divisions as historical data points out. This gives us a mean figure that 1 division equals 10,000 men. This means that a full-force Wehrmacht, in this scenario, could host 2.6 million men (and that's speaking full-force, while we only have 1.8 million men here), which is almost two million less than the real-life battered Wehrmacht of June 1944. This despite the divisions number difference between the scenario and historical data is rather low.
The main mistake lies in the huge difference between a HoI division and a German division. The former is made up of around 10,000-12,000 men, while the German one consists of more than 15,000 men. The OOB for German forces is almost correct in the 1944 scenario both for divisions number and distribution, but it doesn't take into account this difference, which penalizes the German strength by a long shot.
3) THE PROPOSED SOLUTION (done)
We need to create more divisions, even if they didn't exist - the only way to make e.g. 4 German divisions (17,500*4 = 70,000) is to create 7 HoI divs (10,000*7 = 70,000). Following this 7:4 ratio, the 267 divisions ought to become 467. We need to create 200 divisions (done).
467 divisions means 4670 manpower. This means that, on paper, the Wehrmacht could field an army of 4.67 million men. Since we assumed that by June 1944 the Wehrmacht only has 3.5 million at its disposal, this means that the average division is at 70-75% strength. This should be an acceptable value, with divisions on the Eastern front being more damaged and divisions on the Western front being less damaged.
With the total of 467 divisions in mind, we can multiply each regional number of divisions by 1.75 and get a close estimate of how many divisions we should place in each region:
East: 262 divisions
West: 90 divisions
South East: 40 divisions
Denmark&Germany: 10 divisions
Norway&Finland: 20 divisions
Italy: 45 divisions
This gives us a total of 467 divisions, or around 4670 manpower. If we assume that every division is at 70-75% strength (we assumed that avg. damage is 25%-30%) we'd have 3250-3500 manpower: that is, 3.5 million.
Lastly, Germany begins the scenario with a manpower pool of 850. This number should be reduced to 350. (done).