(posting formula before seeing what else was said since I last checked)
Ok, you can get this from your LogicLog_AIMechanic_StrategicReserve.txt file if you have Advanced Logging on, but the formula for the max size of the strategic reserve for a specific AI player is, in terms of the "relative strength" metric (where 1 relative strength is roughly 1 mkI Fighter on high-caps) :
MaxStrategicReserveStrength = 19.8 * AIP * TotalSpecialDifficultyModifier
TotalSpecialDifficultyModifier is used in a lot of contexts, and is:
TotalSpecialDifficultyModifier = TotalPlayerRoleCausedDifficultyModifier * difficultyMultiplier * handicapMultiplier
TotalPlayerRoleCausedDifficultyModifier is basically just the human homeworld count (or "normal" human player count, if that's higher) ; it used to factor in champion count but no longer does. So for most of you this is 1.
handicapMultiplier is just the handicap set for that AI in the lobby. So for most of you this is 1.
difficultyMultiplier is based on the highest AIDiff in the game (since TotalSpecialDifficultyModifier is often used in contexts where there's no particular associated AI player), and is:
if Diff < 7, then Diff *0.15
else if Diff < 8, then Diff = 1 + (Diff-7)/2
else if Diff < 9, then Diff = 1.5 + (Diff-8)*1.5
else if Diff < 10, then Diff = 3 + (Diff-9)*3
So:
For Diff 7 this is 1
For Diff 7.6 this is 1.3
For Diff 8 this is 1.5
For Diff 8.6 this is 2.4
For Diff 9 this is 3
For Diff 9.6 this is 4.8
For Diff 10 this is 6
So on Diff 7.6 on a single-HW game with no handicaps, a static 200-AIP intensity for strategic reserve translates to 19.8 * 200 * 1.3 = 5148 relative strength. So about 5 caps of MkV fleet ships.
On Diff 8.6 it would be 19.8 * 200 * 2.4 = 9504, or between 9 and 10 caps of MkV fleet ships.
And so on, until you reach paintown