From what I have gathered, an OBA module is based upon a battery which varied from 4 to 6 guns for normal artillery (the really heavy stuff could have 3 or even as low as 2 guns in a battery). 4 was the most common number, with usually 12 to a battalion (3 batteries).
Exceptions, ignoring infantry/AT or AA guns:
Late war VG divisions had battalions of 7.5cm guns with 6 to a battery, 18 to a battalion as substitutes for 10.5 cm lFH units with 12 to a battalion.
US infantry regimental batteries with 6 M3 105mm guns.
British 25lbr batteries had 2 troops of 4 guns each for 8 per battery, 24 per regiment (battalion equivalent).
Soviet 120mm mortars which were used more as artillery than mortars had initially 4, quickly changed to 6 and often had 7 (!) tubes by late war in the regimental battery.
Soviet 76mm guns were in 4 gun batteries but had from 3 to 5 batteries per regiment/battalion, 5 being the most common post '42 for a total of 20 guns.
US armoured artillery (SP) batteries had 6 M7 for 18 per battalion vs 12 M2 towed guns in infantry divisions, I suppose to compensate for the lack of a 155mm battalion that the infantry division had.
German FlaK:
Light (2cm) batteries could have 9 or 12 FlaK 30/38 in 3/4 troops (platoons) of 4/3 guns each.
Medium (3.7cm) usually had 9 in 3 troops of 3 each.
Heavy (8.8cm) had 6 8.8cm and 3/4 2cm in 3 heavy (8.8cm) troops (2 guns) and a single troop of 2cm (3/4 guns).
One thing, apart from having 6 8.8cm guns vs 4 10.5cm guns is that a FlaK 18/36/37 had a much higher rate of fire (15-20 rpm) than the 10.5 cm (4-6 rpm), roughly 3 times the RoF. While that would have been impractical in aimed fire vs direct point targets, against an area target as a barrage it was quite practical. I recently viewed a clip showing an 88 firing and was quite surprised at the rate, literally a round every 2 or 3 seconds. Though the Germans did not have VT (variable timed, aka proximity) fuses they did have good mechanical fuses and could lay down a reasonable airburst barrage, often commented upon by US and British soldiers.
Even if only firing the same X number of rounds per gun, I would guess that a 8.8cm FlaK barrage would be more effective than a 10.5cm lFH against all except the most dug in troops as more metal per second will get more enemy before they have a chance to find cover in addition to 50% more guns. So if you have a historical situation where the artillery support was heavy FlaK then you might consider treating as 100+ in ASL terms.