Zum Thema Dach beim T34, in der Wiki steht dazu, dass jeder Schuss, wenn er einen Winkel von 70° unterschreitet, apprallt.
Also 10° Treffer nicht möglich mit Kaliber kleiner 3 x Dachpanzerung (34mm denke ich), also muss das Kaliber min 102mm sein. Also sollte der AMX 13 90 hier nicht durchkommen, es sei denn er stand erhöht und hatte einen besseren Winkel.
Hier die Quelle:
Ricochet
If the normalized impact angle of an AP, APCR or HEAT shell on the target's armour exceeds 70°, a ricochet (also called a bounce) occurs and the shell is deflected off the target without causing any damage. A ricochet can also occur on the hull armour after penetrating spaced armour.
As mentioned above, impact angle is not taken into account when hitting external modules except the gun, so a ricochet off those is impossible.
A ricochet off terrain features, buildings or wrecks is impossible.
Overmatch
If the shell's
caliber is over 3 times greater than the nominal thickness of the armour,
shell normalization is increased by that factor. For example, hitting 20mm of armour with a 120mm shell, your caliber overmatches the armour by a factor of six, so your shell is normalized six times more than it would be by default.
Given a minimum normalization amount of 8° for AP and APCR shells, in cases of overmatch your impact angle is effectively normalized by at least 24°. Since the actual impact angle cannot exceed 90°, in case of overmatch the normalized impact angle cannot be greater than 66°. That means that a ricochet at the point of impact becomes impossible. Note that if you impact spaced armour first, even if you penetrate that your shell may still ricochet off the underlying hull armour.
Naturally, in cases where no shell normalization occurs (HE and HEAT shells or external module hits), overmatch plays no role.