25mm penetration by a 50 cal is at short range and 0 degrees inclination - neither of which any aircraft is going to get.
Most likely the a/c will be at a high inclination - a 30 degree dive is a steep dice, and is at 60 degrees to teh horizontal - which simplistically a tank top armour will be.
And an a/c is not likely to be doing that closer than a couple of hundred meters if it wants to pull out and not crash!
Here’s a penetration table I found - likely for most a/c 50 cal’s 13mm is the best they could hope for under PERFECT combat conditions - (60 deg inclination to vertical = 30 degrees in this table, and at 250m).
In real life such perfect conditions do not apply - they would be at longer ranges and likely even more inclination.
